Pause drawing when not visible

 Bug: 5594608
 If onPause is called or if the view or view's window is no longer
 visible, pause webview drawing. Calls to onDraw will continue to work,
 but animations and other continual drawing will stop

Change-Id: I11640f087852d1a9a33b945ff72297fab1d25b94

Author: jreck

core/java/android/webkit/WebView.java

@@ -3254,6 +3254,26 @@ public void onPause() {
             if (mHTML5VideoViewProxy != null) {
                 mHTML5VideoViewProxy.pauseAndDispatch();
             }
+            if (mNativeClass != 0) {
+                nativeSetPauseDrawing(mNativeClass, true);
+            }
+        }
+    }
+
+    @Override
+    protected void onWindowVisibilityChanged(int visibility) {
+        super.onWindowVisibilityChanged(visibility);
+        updateDrawingState();
+    }
+
+    void updateDrawingState() {
+        if (mNativeClass == 0 || mIsPaused) return;
+        if (getWindowVisibility() != VISIBLE) {
+            nativeSetPauseDrawing(mNativeClass, true);
+        } else if (getVisibility() != VISIBLE) {
+            nativeSetPauseDrawing(mNativeClass, true);
+        } else {
+            nativeSetPauseDrawing(mNativeClass, false);
         }
     }
 
@@ -3265,6 +3285,9 @@ public void onResume() {
         if (mIsPaused) {
             mIsPaused = false;
             mWebViewCore.sendMessage(EventHub.ON_RESUME);
+            if (mNativeClass != 0) {
+                nativeSetPauseDrawing(mNativeClass, false);
+            }
         }
     }
 
@@ -5599,6 +5622,7 @@ protected void onVisibilityChanged(View changedView, int visibility) {
         if (visibility != View.VISIBLE && mZoomManager != null) {
             mZoomManager.dismissZoomPicker();
         }
+        updateDrawingState();
     }
 
     /**
@@ -8403,6 +8427,9 @@ public void handleMessage(Message msg) {
                         setNewPicture(mDelaySetPicture, true);
                         mDelaySetPicture = null;
                     }
+                    if (mIsPaused) {
+                        nativeSetPauseDrawing(mNativeClass, true);
+                    }
                     break;
                 case UPDATE_TEXTFIELD_TEXT_MSG_ID:
                     // Make sure that the textfield is currently focused
@@ -9584,4 +9611,5 @@ private native int      nativeScrollableLayer(int x, int y, Rect scrollRect,
      * See {@link ComponentCallbacks2} for the trim levels and descriptions
      */
     private static native void     nativeOnTrimMemory(int level);
+    private static native void nativeSetPauseDrawing(int instance, boolean pause);
 }