Adding accessibility delegate mechanism for backwards compatibility support.

1. Added an AccessibilityDelegate class in View which can be set by
   a client that wants to cutomize accessibility behavior via
   composition as opposed to inheritance. Insead overriding a new method in
   View thus being bound to the API version that introduced this
   method a developer can conditionally inject the accessibility
   customization if the platform API version is heigh enough. The
   developer will have to override the method of interest of the
   delegate. The default implementation of the delegate methods is
   the same as that of View in the case that there is no delegate
   set. If a delegate is set calling an accessibility related method
   on View will be handed off to the corresponsing method of the
   delegate.

bug:5259555

Change-Id: I00e750e22e5e7164a1b571cb3d12ecaf4ab93db4

Author: sganov

api/current.txt

@@ -22950,6 +22950,7 @@ package android.view {
     method public void scrollTo(int, int);
     method public void sendAccessibilityEvent(int);
     method public void sendAccessibilityEventUnchecked(android.view.accessibility.AccessibilityEvent);
+    method public void setAccessibilityDelegate(android.view.View.AccessibilityDelegate);
     method public void setActivated(boolean);
     method public void setAlpha(float);
     method public void setAnimation(android.view.animation.Animation);
@@ -23126,6 +23127,17 @@ package android.view {
     field public static android.util.Property Y;
   }
 
+  public static class View.AccessibilityDelegate {
+    ctor public View.AccessibilityDelegate();
+    method public boolean dispatchPopulateAccessibilityEvent(android.view.View, android.view.accessibility.AccessibilityEvent);
+    method public void onInitializeAccessibilityEvent(android.view.View, android.view.accessibility.AccessibilityEvent);
+    method public void onInitializeAccessibilityNodeInfo(android.view.View, android.view.accessibility.AccessibilityNodeInfo);
+    method public void onPopulateAccessibilityEvent(android.view.View, android.view.accessibility.AccessibilityEvent);
+    method public boolean onRequestSendAccessibilityEvent(android.view.ViewGroup, android.view.View, android.view.accessibility.AccessibilityEvent);
+    method public void sendAccessibilityEvent(android.view.View, int);
+    method public void sendAccessibilityEventUnchecked(android.view.View, android.view.accessibility.AccessibilityEvent);
+  }
+
   public static class View.BaseSavedState extends android.view.AbsSavedState {
     ctor public View.BaseSavedState(android.os.Parcel);
     ctor public View.BaseSavedState(android.os.Parcelable);