Move destroying the web view to the WVC thread (previously it was on the UI thread)

Change-Id: I5a48734c6a244eadd1d60659f8e02ebb889a8fc1
diff --git a/core/java/android/webkit/WebViewCore.java b/core/java/android/webkit/WebViewCore.java
index ce45373..c87e5a5 100644
--- a/core/java/android/webkit/WebViewCore.java
+++ b/core/java/android/webkit/WebViewCore.java
@@ -856,6 +856,7 @@
                                 mBrowserFrame = null;
                                 mSettings.onDestroyed();
                                 mNativeClass = 0;
+                                mWebView = null;
                             }
                             break;
 
@@ -1406,7 +1407,6 @@
                         Message.obtain(null, EventHub.RESUME_TIMERS));
             }
             mEventHub.blockMessages();
-            mWebView = null;
         }
     }