[HR] Documentation cleanup (#7370)

* Documentation cleanup

* Typo fix

lib/ui/isolate_name_server.dart

@@ -4,31 +4,67 @@
 
 part of dart.ui;
 
-/// Contains methods to allow for simple sharing of SendPorts across isolates.
-abstract class IsolateNameServer {
-  /// Looks up the [SendPort] associated with a given name. Returns null
-  /// if the name does not exist.
+/// Static methods to allow for simple sharing of [SendPort]s across [Isolate]s.
+///
+/// All isolates share a global mapping of names to ports. An isolate can
+/// register a [SendPort] with a given name using [registerPortWithName];
+/// another isolate can then look up that port using [lookupPortByName].
+///
+/// To create a [SendPort], first create a [ReceivePort], then use
+/// [ReceivePort.sendPort].
+///
+/// Since multiple isolates can each obtain the same [SendPort] associated with
+/// a particular [ReceivePort], the protocol built on top of this mechanism
+/// should typically consist of a single message. If more elaborate two-way
+/// communication or multiple-message communication is necessary, it is
+/// recommended to establish a separate communication channel in that first
+/// message (e.g. by passing a dedicated [SendPort]).
+class IsolateNameServer {
+  // This class is only a namespace, and should not be instantiated or
+  // extended directly.
+  factory IsolateNameServer._() => null;
+
+  /// Looks up the [SendPort] associated with a given name.
+  ///
+  /// Returns null if the name does not exist. To register the name in the first
+  /// place, consider [registerPortWithName].
   ///
-  /// `name` must not be null.
+  /// The `name` argument must not be null.
   static SendPort lookupPortByName(String name) {
     assert(name != null, "'name' cannot be null.");
     return _lookupPortByName(name);
   }
 
-  /// Registers a SendPort with a given name. Returns true if registration is
-  /// successful, false if the name entry already exists.
+  /// Registers a [SendPort] with a given name.
+  ///
+  /// Returns true if registration is successful, and false if the name entry
+  /// already existed (in which case the earlier registration is left
+  /// unchanged). To remove a registration, consider [removePortNameMapping].
+  ///
+  /// Once a port has been registered with a name, it can be obtained from any
+  /// [Isolate] using [lookupPortByName].
   ///
-  /// `port` and `name` must not be null.
+  /// Multiple isolates should avoid attempting to register ports with the same
+  /// name, as there is an inherent race condition in doing so.
+  ///
+  /// The `port` and `name` arguments must not be null.
   static bool registerPortWithName(SendPort port, String name) {
     assert(port != null, "'port' cannot be null.");
     assert(name != null, "'name' cannot be null.");
     return _registerPortWithName(port, name);
   }
 
-  /// Removes a name to SendPort mapping given a name. Returns true if the
-  /// mapping was successfully removed, false if the mapping does not exist.
+  /// Removes a name-to-[SendPort] mapping given its name.
+  ///
+  /// Returns true if the mapping was successfully removed, false if the mapping
+  /// did not exist. To add a registration, consider [registerPortWithName].
+  ///
+  /// Generally, removing a port name mapping is an inherently racy operation
+  /// (another isolate could have obtained the name just prior to the name being
+  /// removed, and thus would still be able to communicate over the port even
+  /// after it has been removed).
   ///
-  /// `name` must not be null.
+  /// The `name` argument must not be null.
   static bool removePortNameMapping(String name) {
     assert(name != null, "'name' cannot be null.");
     return _removePortNameMapping(name);

lib/ui/painting.dart

@@ -1522,10 +1522,10 @@ class _ImageInfo {
 /// [Canvas.drawImage].
 @pragma('vm:entry-point')
 class Image extends NativeFieldWrapperClass2 {
-  /// This class is created by the engine, and should not be instantiated
-  /// or extended directly.
-  ///
-  /// To obtain an [Image] object, use [instantiateImageCodec].
+  // This class is created by the engine, and should not be instantiated
+  // or extended directly.
+  //
+  // To obtain an [Image] object, use [instantiateImageCodec].
   @pragma('vm:entry-point')
   Image._();
 
@@ -1587,13 +1587,20 @@ class FrameInfo extends NativeFieldWrapperClass2 {
 }
 
 /// A handle to an image codec.
+///
+/// This class is created by the engine, and should not be instantiated
+/// or extended directly.
+///
+/// To obtain an instance of the [Codec] interface, see
+/// [instantiateImageCodec].
 @pragma('vm:entry-point')
 class Codec extends NativeFieldWrapperClass2 {
-  /// This class is created by the engine, and should not be instantiated
-  /// or extended directly.
-  ///
-  /// To obtain an instance of the [Codec] interface, see
-  /// [instantiateImageCodec].
+  //
+  // This class is created by the engine, and should not be instantiated
+  // or extended directly.
+  //
+  // To obtain an instance of the [Codec] interface, see
+  // [instantiateImageCodec].
   @pragma('vm:entry-point')
   Codec._();
 
@@ -1656,8 +1663,8 @@ String _instantiateImageCodec(Uint8List list, _Callback<Codec> callback, _ImageI
 
 /// Loads a single image frame from a byte array into an [Image] object.
 ///
-/// This is a convenience wrapper around [instantiateImageCodec].
-/// Prefer using [instantiateImageCodec] which also supports multi frame images.
+/// This is a convenience wrapper around [instantiateImageCodec]. Prefer using
+/// [instantiateImageCodec] which also supports multi frame images.
 void decodeImageFromList(Uint8List list, ImageDecoderCallback callback) {
   _decodeImageFromListAsync(list, callback);
 }

lib/ui/plugins.dart

@@ -4,10 +4,10 @@
 
 part of dart.ui;
 
-/// An wrapper for a raw callback handle.
+/// A wrapper for a raw callback handle.
+///
+/// This is the return type for [PluginUtilities.getCallbackHandle].
 class CallbackHandle {
-  final int _handle;
-
   /// Create an instance using a raw callback handle.
   ///
   /// Only values produced by a call to [CallbackHandle.toRawHandle] should be
@@ -15,20 +15,31 @@ class CallbackHandle {
   CallbackHandle.fromRawHandle(this._handle)
       : assert(_handle != null, "'_handle' must not be null.");
 
-  /// Get the raw callback handle to pass over a [MethodChannel] or isolate
-  /// port.
+  final int _handle;
+
+  /// Get the raw callback handle to pass over a [MethodChannel] or [SendPort]
+  /// (to pass to another [Isolate]).
   int toRawHandle() => _handle;
 
   @override
-  int get hashCode => _handle;
+  bool operator ==(dynamic other) {
+    if (runtimeType != other.runtimeType)
+      return false;
+    final CallbackHandle typedOther = other;
+    return _handle == typedOther._handle;
+  }
 
   @override
-  bool operator ==(dynamic other) =>
-      (other is CallbackHandle) && (_handle == other._handle);
+  int get hashCode => _handle.hashCode;
 }
 
 /// Functionality for Flutter plugin authors.
-abstract class PluginUtilities {
+///
+/// See also:
+///
+///  * [IsolateNameServer], which provides utilities for dealing with
+///    [Isolate]s.
+class PluginUtilities {
   // This class is only a namespace, and should not be instantiated or
   // extended directly.
   factory PluginUtilities._() => null;
@@ -41,7 +52,7 @@ abstract class PluginUtilities {
   /// Get a handle to a named top-level or static callback function which can
   /// be easily passed between isolates.
   ///
-  /// `callback` must not be null.
+  /// The `callback` argument must not be null.
   ///
   /// Returns a [CallbackHandle] that can be provided to
   /// [PluginUtilities.getCallbackFromHandle] to retrieve a tear-off of the
@@ -58,7 +69,7 @@ abstract class PluginUtilities {
   /// Get a tear-off of a named top-level or static callback represented by a
   /// handle.
   ///
-  /// `handle` must not be null.
+  /// The `handle` argument must not be null.
   ///
   /// If `handle` is not a valid handle returned by
   /// [PluginUtilities.getCallbackHandle], null is returned. Otherwise, a