[WebView] Add a new flushVisualState API to AwContents.

android_webview/java/src/org/chromium/android_webview/AwContents.java

Index: android_webview/java/src/org/chromium/android_webview/AwContents.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContents.java b/android_webview/java/src/org/chromium/android_webview/AwContents.java
index 4d80be73e6d07d234a2cfeef69823b3e5675638d..9b59dbe22adbc917aa72b6b6cd43b180d5897832 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -94,6 +94,8 @@ public class AwContents implements SmartClipProvider {
     // produce little visible difference.
     private static final float ZOOM_CONTROLS_EPSILON = 0.007f;
 
+    private static final String BLANK_URL = "about:blank";
+
     /**
      * WebKit hit test related data strcutre. These are used to implement
      * getHitTestResult, requestFocusNodeHref, requestImageRef methods in WebView.
@@ -182,6 +184,15 @@ public class AwContents implements SmartClipProvider {
         }
     }
 
+    /**
+     * Callback used when flushing the visual state, see {@link #flushVisualState}.
+     */
+    @VisibleForTesting
+    public abstract static class VisualStateFlushCallback {
+        public abstract void onComplete();
+        public abstract void onFailure(int reason);
+    }
+
     private long mNativeAwContents;
     private final AwBrowserContext mBrowserContext;
     private ViewGroup mContainerView;
@@ -256,6 +267,9 @@ public class AwContents implements SmartClipProvider {
     // when in this state.
     private boolean mTemporarilyDetached;
 
+    // This flag indicates that we're currently loading BLANK_URL from loadBlankNow.
+    private boolean mIsLoadingBlankNow = false;
+
     // True when this AwContents has been destroyed.
     // Do not use directly, call isDestroyed() instead.
     private boolean mIsDestroyed = false;
@@ -552,6 +566,34 @@ public class AwContents implements SmartClipProvider {
     }
 
     /**
+     * Extension of {@link AwWebContentsObserver} that adds functionality that {@link AwContents}
+     * encapsulates.
+     */
+    private class AwContentsAwWebContentsObserver extends AwWebContentsObserver {
+        public AwContentsAwWebContentsObserver(
+                WebContents webContents, AwContentsClient awContentsClient) {
+            super(webContents, awContentsClient);
+        }
+
+        @Override
+        public void didNavigateMainFrame(String url, String baseUrl,
+                boolean isNavigationToDifferentPage, boolean isFragmentNavigation) {
+            super.didNavigateMainFrame(
+                    url, baseUrl, isNavigationToDifferentPage, isFragmentNavigation);
+            // Waiting for didNavigateMainFrame before flashing ensures that the flush callback will

[mkosiba (inactive), 2015/01/19 11:15:58]

nit: before flushing?

[Ignacio Solla, 2015/01/19 18:26:41]

Done.

+            // not be received before BLANK_URL has made it into the screen.
+            flushVisualStateIfLoadingBlankNow(url);
+        }
+
+        @Override
+        public void didFailLoad(boolean isProvisionalLoad, boolean isMainFrame, int errorCode,
+                String description, String failingUrl) {
+            super.didFailLoad(isProvisionalLoad, isMainFrame, errorCode, description, failingUrl);
+            flushVisualStateIfLoadingBlankNow(failingUrl);
+        }
+    }
+
+    /**
      * @param browserContext the browsing context to associate this view contents with.
      * @param containerView the view-hierarchy item this object will be bound to.
      * @param context the context to use, usually containerView.getContext().
@@ -835,7 +877,7 @@ public class AwContents implements SmartClipProvider {
         if (mWebContentsObserver != null) {
             mWebContentsObserver.detachFromWebContents();
         }
-        mWebContentsObserver = new AwWebContentsObserver(mWebContents, mContentsClient);
+        mWebContentsObserver = new AwContentsAwWebContentsObserver(mWebContents, mContentsClient);
     }
 
     /**
@@ -978,6 +1020,11 @@ public class AwContents implements SmartClipProvider {
         return mNavigationController;
     }
 
+    @VisibleForTesting
+    public Context getContext() {

[mkosiba (inactive), 2015/01/19 11:15:58]

I don't think you need this, the base test class has a getActivity() method

[Ignacio Solla, 2015/01/19 18:26:41]

Done.

+        return mContext;
+    }
+
     // Can be called from any thread.
     public AwSettings getSettings() {
         return mSettings;
@@ -1144,6 +1191,38 @@ public class AwContents implements SmartClipProvider {
     }
 
     /**
+     * Loads "about:blank" and draws the background color specified by
+     * {@link AwContents#setBackgroundColor(int)} immediately without having to wait for the
+     * asynchronous load to complete ({@link AwContentsClient#onPageFinished(String)}).
+     *
+     * <p>This API is useful when recycling container views and want to clear the contents from the
+     * old page immediately.
+     */
+    public void loadBlankNow() {
+        if (mIsLoadingBlankNow) {
+            return;
+        }
+        loadUrl(new LoadUrlParams(BLANK_URL));
+        mIsLoadingBlankNow = true;
+    }
+
+    private void flushVisualStateIfLoadingBlankNow(String url) {
+        if (mIsLoadingBlankNow && BLANK_URL.equals(url)) {
+            flushVisualState(new VisualStateFlushCallback() {
+                @Override
+                public void onFailure(int reason) {
+                    mIsLoadingBlankNow = false;

[mkosiba (inactive), 2015/01/19 11:15:58]

I think Bo mentioned you need to postInvalidateOnAnimation from here

[Ignacio Solla, 2015/01/19 18:26:41]

I propagate this bit to BVR. I'll ask Bo if we still need to postInvalidate
given that BVR ensures continues invalidation while the bit is set.

[Ignacio Solla, 2015/01/19 18:31:57]

Bo confirmed offline that EnsureContinuousInvalidate is enough and already
handles this, so we don't need an additional call to postInvalidate when we
unset the bit.

+                }
+
+                @Override
+                public void onComplete() {
+                    mIsLoadingBlankNow = false;
+                }
+            });
+        }
+    }
+
+    /**
      * Load url without fixing up the url string. Consumers of ContentView are responsible for
      * ensuring the URL passed in is properly formatted (i.e. the scheme has been added if left
      * off during user input).
@@ -1243,7 +1322,9 @@ public class AwContents implements SmartClipProvider {
         // Do not ask the ContentViewCore for the background color, as it will always
         // report white prior to initial navigation or post destruction,  whereas we want
         // to use the client supplied base value in those cases.
-        if (isDestroyed() || !mContentsClient.isCachedRendererBackgroundColorValid()) {
+        // When loading BLANK_URL we want to draw the client supplied base color immediately.
+        if (isDestroyed() || !mContentsClient.isCachedRendererBackgroundColorValid()
+                || mIsLoadingBlankNow) {
             return mBaseBackgroundColor;
         }
         return mContentsClient.getCachedRendererBackgroundColor();
@@ -2020,6 +2101,22 @@ public class AwContents implements SmartClipProvider {
         if (!isDestroyed()) nativeSetJsOnlineProperty(mNativeAwContents, networkUp);
     }
 
+    /**
+     * Flush the visual state.
+     *
+     * Flushing the visual state means queuing a callback in Blink that will be invoked when the
+     * contents of the DOM tree at the moment that the callback was enqueued (or later) are drawn
+     * into the screen. In other words, the following events need to happen before the callback is
+     * invoked:
+     * 1. The DOM tree is committed becoming the pending tree - see ThreadProxy::BeginMainFrame
+     * 2. The pending tree is activated becoming the active tree
+     * 3. A frame swap happens that draws the active tree into the screen
+     */
+    @VisibleForTesting
+    public void flushVisualState(VisualStateFlushCallback callback) {
+        nativeFlushVisualState(mNativeAwContents, callback);
+    }
+
     //--------------------------------------------------------------------------------------------
     //  Methods called from native via JNI
     //--------------------------------------------------------------------------------------------
@@ -2123,6 +2220,15 @@ public class AwContents implements SmartClipProvider {
         mContentsClient.getCallbackHelper().postOnNewPicture(mPictureListenerContentProvider);
     }
 
+    @CalledByNative
+    public static void flushVisualStateCallback(VisualStateFlushCallback callback, int value) {
+        if (value == 0) {
+            callback.onComplete();
+        } else {
+            callback.onFailure(value);
+        }
+    }
+
     // Called as a result of nativeUpdateLastHitTestData.
     @CalledByNative
     private void updateHitTestData(
@@ -2337,8 +2443,9 @@ public class AwContents implements SmartClipProvider {
 
         @Override
         public void onDraw(Canvas canvas) {
-            if (isDestroyed()) {
-                TraceEvent.instant("EarlyOut_destroyed");
+            if (isDestroyed() || mIsLoadingBlankNow) {
+                String trace = isDestroyed() ? "EarlyOut_destroyed" : "EarlyOut_loadingBlank";
+                TraceEvent.instant(trace);
                 canvas.drawColor(getEffectiveBackgroundColor());
                 return;
             }
@@ -2688,6 +2795,8 @@ public class AwContents implements SmartClipProvider {
     private native long nativeGetAwDrawGLViewContext(long nativeAwContents);
     private native long nativeCapturePicture(long nativeAwContents, int width, int height);
     private native void nativeEnableOnNewPicture(long nativeAwContents, boolean enabled);
+    private native void nativeFlushVisualState(
+            long nativeAwContents, VisualStateFlushCallback callback);
     private native void nativeClearView(long nativeAwContents);
     private native void nativeSetExtraHeadersForUrl(long nativeAwContents,
             String url, String extraHeaders);