[Remoting Android] JniGlDisplayHandler calls invalidate() on UI thread

remoting/android/java/src/org/chromium/chromoting/jni/GlDisplay.java

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chromoting.jni;
 
 import android.graphics.Matrix;
 import android.graphics.PointF;
 import android.view.Surface;
 import android.view.SurfaceHolder;
 
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
 import org.chromium.chromoting.DesktopView;
 import org.chromium.chromoting.Event;
 import org.chromium.chromoting.InputFeedbackRadiusMapper;
 import org.chromium.chromoting.RenderStub;
 import org.chromium.chromoting.SizeChangedEventParameter;
 
 /**
  * This class is a RenderStub implementation that uses the OpenGL renderer in native code to render
  * the remote desktop. The lifetime of this class is managed by the native JniGlDisplayHandler.
  *
  * This class works entirely on the UI thread:
- *  Functions should all be called on UI.
- *  Events will only be triggered on UI.
+ *  All functions, including callbacks from native code are called only on UI thread.
  */
 @JNINamespace("remoting")
 public class GlDisplay implements SurfaceHolder.Callback, RenderStub {
     private final Event.Raisable<SizeChangedEventParameter> mOnClientSizeChanged =
             new Event.Raisable<>();
     private final Event.Raisable<SizeChangedEventParameter> mOnHostSizeChanged =
             new Event.Raisable<>();
     private final Event.Raisable<Void> mOnCanvasRendered = new Event.Raisable<>();
 
-    private volatile long mNativeJniGlDisplay;
+    private long mNativeJniGlDisplay;
     private InputFeedbackRadiusMapper mFeedbackRadiusMapper;
     private float mScaleFactor = 0;
 
     private GlDisplay(long nativeJniGlDisplay) {
         mNativeJniGlDisplay = nativeJniGlDisplay;
     }
 
     /**
-     * Invalidates this object and disconnects from the native display handler. Called on the
-     * display thread by the native code.
+     * Invalidates this object and disconnects from the native display handler.
      */
     @CalledByNative
     private void invalidate() {
         mNativeJniGlDisplay = 0;
     }
 
     /**
      * Notifies the OpenGL renderer that a surface for OpenGL to draw is created.
      * @param holder the surface holder that holds the surface.
      */
@@ skipping 134 matching lines @@
     private native void nativeOnSurfaceDestroyed(long nativeJniGlDisplayHandler);
     private native void nativeOnPixelTransformationChanged(long nativeJniGlDisplayHandler,
                                                            float[] matrix);
     private native void nativeOnCursorPixelPositionChanged(long nativeJniGlDisplayHandler,
                                                            float x, float y);
     private native void nativeOnCursorInputFeedback(long nativeJniGlDisplayHandler,
                                                     float x, float y, float diameter);
     private native void nativeOnCursorVisibilityChanged(long nativeJniGlDisplayHandler,
                                                         boolean visible);
 }