Document //flutter/shell/common/engine. (#9769)

shell/common/engine.cc

@@ -450,8 +450,8 @@ void Engine::UpdateIsolateDescription(const std::string isolate_name,
   delegate_.UpdateIsolateDescription(isolate_name, isolate_port);
 }
 
-void Engine::SetNeedsReportTimings(bool value) {
-  delegate_.SetNeedsReportTimings(value);
+void Engine::SetNeedsReportTimings(bool needs_reporting) {
+  delegate_.SetNeedsReportTimings(needs_reporting);
 }
 
 FontCollection& Engine::GetFontCollection() {

shell/common/platform_view.h

@@ -333,7 +333,8 @@ class PlatformView {
 
   //----------------------------------------------------------------------------
   /// @brief      Used by the framework to tell the embedder to apply the
-  ///             specified semantics node updates.
+  ///             specified semantics node updates. The default implementation
+  ///             of this method does nothing.
   ///
   /// @see        SemanticsNode, SemticsNodeUpdates,
   ///             CustomAccessibilityActionUpdates