[Android] Add proxy for Java-based WebContentsObservers

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 9661001334f919f008cfd384bbacae71d7cc8a0d..2494286031b2a0e78ecc01cdd21ff0759d322df7 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -845,7 +845,7 @@ public class AwContents implements SmartClipProvider,
 
     private void installWebContentsObserver() {
         if (mWebContentsObserver != null) {
-            mWebContentsObserver.detachFromWebContents();
+            mWebContentsObserver.destroy();
         }
         mWebContentsObserver = new AwWebContentsObserver(mWebContents, mContentsClient);
     }
@@ -956,7 +956,7 @@ public class AwContents implements SmartClipProvider,
         if (mCleanupReference != null) {
             assert mNativeAwContents != 0;
 
-            mWebContentsObserver.detachFromWebContents();
+            mWebContentsObserver.destroy();
             mWebContentsObserver = null;
             mContentViewCore.destroy();
             mContentViewCore = null;