[Android] Add proxy for Java-based WebContentsObservers

content/public/android/javatests/src/org/chromium/content/browser/WebContentsObserverAndroidTest.java

 // Copyright 2014 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.content.browser;
 
 import org.chromium.base.ThreadUtils;
 import org.chromium.base.test.util.DisabledTest;
 import org.chromium.base.test.util.UrlUtils;
 import org.chromium.content.browser.test.util.CallbackHelper;
 import org.chromium.content_public.browser.LoadUrlParams;
 import org.chromium.content_public.browser.WebContents;
+import org.chromium.content_public.browser.WebContentsObserver;
 import org.chromium.content_shell_apk.ContentShellActivity;
 import org.chromium.content_shell_apk.ContentShellTestBase;
 
 import java.util.concurrent.Callable;
 
 /**
  * Tests for the WebContentsObserver APIs.
  */
 public class WebContentsObserverAndroidTest extends ContentShellTestBase {
     private static final String URL = UrlUtils.encodeHtmlDataUri(
@@ skipping 43 matching lines @@
         getInstrumentation().runOnMainSync(new Runnable() {
             @Override
             public void run() {
                 getContentViewCore().getWebContents().getNavigationController()
                         .loadUrl(new LoadUrlParams(URL));
             }
         });
         observer.getDidFirstVisuallyNonEmptyPaintCallbackHelper().waitForCallback(callCount);
     }
 }