[WebView] Add a new flushVisualState API to AwContents.

android_webview/native/aw_contents.h

Index: android_webview/native/aw_contents.h
diff --git a/android_webview/native/aw_contents.h b/android_webview/native/aw_contents.h
index 4a4afbbe981f25b935f9bc46690c6ee6b8fa4a4e..79abe642b42b5933525590c1a41106a312aad088 100644
--- a/android_webview/native/aw_contents.h
+++ b/android_webview/native/aw_contents.h
@@ -127,6 +127,7 @@ class AwContents : public FindHelper::Listener,
   jlong GetAwDrawGLViewContext(JNIEnv* env, jobject obj);
   jlong CapturePicture(JNIEnv* env, jobject obj, int width, int height);
   void EnableOnNewPicture(JNIEnv* env, jobject obj, jboolean enabled);
+  void FlushVisualState(JNIEnv* env, jobject obj, jobject callback);
   void ClearView(JNIEnv* env, jobject obj);
   void SetExtraHeadersForUrl(JNIEnv* env, jobject obj,
                              jstring url, jstring extra_headers);