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
Avoid adding FORWARD_LOCK flag to an updated system app

Consider the following case:
1. An app exists in /system/app or /vendor/app. (i.e, it's a system app)
2. If the app would be updated as a forward-lock app by downloading from
   market(google play), then it would be installed in /data/app-private.
3. Moreover, if it would be updated by the whole system image (i.e, FOTA
   or something like that), then the app would be applied a FORWARD_LOCK
   flag.

The app SHOULD NOT have a FORWARD_LCOK flag. Because the resource path
of such app does not refer to the proper resources to access.

Change-Id: I0750f69a93a3115f4201029796b598507de3555f
Add additional Method that check whether a table is empty or not

Application Devleopers are using queryNumEntries API
implemented by "COUNT(*)" to check whether a table is empty or not.
COUNT(*)  has to process the entire table to compute the result.
But, "EXISTS" can stop after a single matching row has been found.
So, Using "EXISTS" is more faster than "COUNT(*)"
I added new API using "EXISTS" to check whether a table is empty or not

Change-Id: Idcc2633d0a5349c59f41e125cf34c9dc6622cdbe