[Android] Install a WebContentsObserverAndroid in android_webview.

android_webview/java/src/org/chromium/android_webview/AwContentsClient.java

Index: android_webview/java/src/org/chromium/android_webview/AwContentsClient.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContentsClient.java b/android_webview/java/src/org/chromium/android_webview/AwContentsClient.java
index e239b3f2fbad505f76f17d435ced4164db40992a..9f971e291e3511325e2a923291d74a124531171a 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContentsClient.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContentsClient.java
@@ -30,6 +30,8 @@ public abstract class AwContentsClient extends ContentViewClient {
     private final WebContentsDelegateAdapter mWebContentsDelegateAdapter =
             new WebContentsDelegateAdapter();
 
+    private AwWebContentsObserver mWebContentsObserver;
+
     //--------------------------------------------------------------------------------------------
     //                        Adapter for WebContentsDelegate methods.
     //--------------------------------------------------------------------------------------------
@@ -104,8 +106,8 @@ public abstract class AwContentsClient extends ContentViewClient {
         }
     }
 
-    class WebContentsObserverAdapter extends WebContentsObserverAndroid {
-        public WebContentsObserverAdapter(ContentViewCore contentViewCore) {
+    class AwWebContentsObserver extends WebContentsObserverAndroid {
+        public AwWebContentsObserver(ContentViewCore contentViewCore) {
             super(contentViewCore);
         }
 
@@ -127,6 +129,11 @@ public abstract class AwContentsClient extends ContentViewClient {
         }
     }
 
+    void installWebContentsObserver(ContentViewCore contentViewCore) {
+        assert mWebContentsObserver == null;
+        mWebContentsObserver = new AwWebContentsObserver(contentViewCore);
+    }
+
     final AwWebContentsDelegate getWebContentsDelegate()  {
         return mWebContentsDelegateAdapter;
     }