Pause WebKit drawing when WebView loses window focus.

This prevents animations and other live page content from consuming
too many resources while the user is interacting with a popup window.

Bug 5300522

Change-Id: I40fb6d16d56b540c431172052a1ae7fead7109be

Author: adamp

core/java/android/webkit/WebSettings.java

@@ -643,10 +643,10 @@ public boolean getLoadWithOverviewMode() {
 
     /**
      * Set whether the WebView will enable smooth transition while panning or
-     * zooming. If it is true, WebView will choose a solution to maximize the
-     * performance. e.g. the WebView's content may not be updated during the
-     * transition. If it is false, WebView will keep its fidelity. The default
-     * value is false.
+     * zooming or while the window hosting the WebView does not have focus.
+     * If it is true, WebView will choose a solution to maximize the performance.
+     * e.g. the WebView's content may not be updated during the transition.
+     * If it is false, WebView will keep its fidelity. The default value is false.
      */
     public void setEnableSmoothTransition(boolean enable) {
         mEnableSmoothTransition = enable;

core/java/android/webkit/WebView.java

@@ -908,6 +908,9 @@ public void onTrimMemory(int level) {
     // used for serializing asynchronously handled touch events.
     private final TouchEventQueue mTouchEventQueue = new TouchEventQueue();
 
+    // Used to track whether picture updating was paused due to a window focus change.
+    private boolean mPictureUpdatePausedForFocusChange = false;
+
     // Used to notify listeners of a new picture.
     private PictureListener mPictureListener;
     /**
@@ -5570,8 +5573,20 @@ public void onWindowFocusChanged(boolean hasWindowFocus) {
         setActive(hasWindowFocus);
         if (hasWindowFocus) {
             JWebCoreJavaBridge.setActiveWebView(this);
+            if (mPictureUpdatePausedForFocusChange) {
+                WebViewCore.resumeUpdatePicture(mWebViewCore);
+                nativeSetIsScrolling(false);
+                mPictureUpdatePausedForFocusChange = false;
+            }
         } else {
             JWebCoreJavaBridge.removeActiveWebView(this);
+            final WebSettings settings = getSettings();
+            if (settings != null && settings.enableSmoothTransition() &&
+                    mWebViewCore != null && !WebViewCore.isUpdatePicturePaused(mWebViewCore)) {
+                WebViewCore.pauseUpdatePicture(mWebViewCore);
+                nativeSetIsScrolling(true);
+                mPictureUpdatePausedForFocusChange = true;
+            }
         }
         super.onWindowFocusChanged(hasWindowFocus);
     }

core/java/android/webkit/WebViewCore.java

@@ -2107,6 +2107,10 @@ static void resumeUpdatePicture(WebViewCore core) {
         }
     }
 
+    static boolean isUpdatePicturePaused(WebViewCore core) {
+        return core != null ? core.mDrawIsPaused : false;
+    }
+
     //////////////////////////////////////////////////////////////////////////
 
     private void restoreState(int index) {