PointerChange.cancel should have a zero index (#3135)

To make the default state all zeros.

Fixes https://github.com/flutter/flutter/issues/6236

lib/ui/pointer.dart

@@ -6,6 +6,9 @@ part of dart_ui;
 
 /// How the pointer has changed since the last report.
 enum PointerChange {
+  /// The input from the pointer is no longer directed towards this receiver.
+  cancel,
+
   /// The device has started tracking the pointer.
   ///
   /// For example, the pointer might be hovering above the device, having not yet
@@ -26,9 +29,6 @@ enum PointerChange {
 
   /// The pointer has stopped making contact with the device.
   up,
-
-  /// The input from the pointer is no longer directed towards this receiver.
-  cancel,
 }
 
 /// The kind of pointer device.

lib/ui/window/pointer_data.cc

@@ -4,6 +4,8 @@
 
 #include "flutter/lib/ui/window/pointer_data.h"
 
+#include <string.h>
+
 namespace blink {
 
 // If this value changes, update the pointer data unpacking code in hooks.dart.
@@ -13,25 +15,7 @@ static_assert(sizeof(PointerData) == sizeof(int64_t) * kPointerDataFieldCount,
               "PointerData has the wrong size");
 
 void PointerData::Clear() {
-  time_stamp = 0;
-  pointer = 0;
-  change = Change::kCancel;
-  kind = DeviceKind::kTouch;
-  physical_x = 0.0;
-  physical_y = 0.0;
-  buttons = 0;
-  obscured = 0;
-  pressure = 0.0;
-  pressure_min = 0.0;
-  pressure_max = 0.0;
-  distance = 0.0;
-  distance_max = 0.0;
-  radius_major = 0.0;
-  radius_minor = 0.0;
-  radius_min = 0.0;
-  radius_max = 0.0;
-  orientation = 0.0;
-  tilt = 0.0;
+  memset(this, 0, sizeof(PointerData));
 }
 
 }  // namespace blink

lib/ui/window/pointer_data.h

@@ -13,12 +13,12 @@ namespace blink {
 struct alignas(8) PointerData {
   // Must match the PointerChange enum in pointer.dart.
   enum class Change : int64_t {
+    kCancel,
     kAdd,
     kRemove,
     kDown,
     kMove,
     kUp,
-    kCancel,
   };
 
   // Must match the PointerDeviceKind enum in pointer.dart.

shell/platform/android/io/flutter/view/FlutterView.java

@@ -261,12 +261,12 @@ public class FlutterView extends SurfaceView
     }
 
     // Must match the PointerChange enum in pointer.dart.
-    private static final int kPointerChangeAdd = 0;
-    private static final int kPointerChangeRemove = 1;
-    private static final int kPointerChangeDown = 2;
-    private static final int kPointerChangeMove = 3;
-    private static final int kPointerChangeUp = 4;
-    private static final int kPointerChangeCancel = 5;
+    private static final int kPointerChangeCancel = 0;
+    private static final int kPointerChangeAdd = 1;
+    private static final int kPointerChangeRemove = 2;
+    private static final int kPointerChangeDown = 3;
+    private static final int kPointerChangeMove = 4;
+    private static final int kPointerChangeUp = 5;
 
     // Must match the PointerDeviceKind enum in pointer.dart.
     private static final int kPointerDeviceKindTouch = 0;