Fix deadlock of WebViewCoreThread

There was a deadlock in destroy process.
Investigation showed that WebViewCoreThread is waiting some
callbacks but in this case WebViewCoreThread can not resume
itself not to call notify method.

Flow:
1. CallbackProxy.sendMessageToUiThreadSync
2. WebViewClassic.destroy()
3. CallbackProxy.blockMessages()
4. CallbackProxy.handleMessage is called via MainThread
5. The WebViewCoreThread deadlock is occured.

The cases we have to call notify method are followings.
OVERRIDE_URL
CREATE_WINDOW
SAVE_PASSWORD
NOTIFY
OPEN_FILE_CHOOSER
JS_ALERT
JS_CONFIRM
JS_PROMPT
JS_UNLOAD
JS_TIMEOUT

Change-Id: I9d95ae500bf6338d77b32b5fa15de7cff5720d0f

core/java/android/webkit/CallbackProxy.java

@@ -305,7 +305,12 @@ class CallbackProxy extends Handler {
         // in the UI thread. The WebViewClient and WebChromeClient functions
         // that check for a non-null callback are ok because java ensures atomic
         // 32-bit reads and writes.
-        if (messagesBlocked()) return;
+        if (messagesBlocked()) {
+            synchronized (this) {
+                notify();
+            }
+            return;
+        }
         switch (msg.what) {
             case PAGE_STARTED:
                 String startedUrl = msg.getData().getString("url");