Hide insertion handles when deleting text

Insertion text handles should be hidden when the underlying text changes. As
such, add a hook to notify the AdapterInputConnection embedder of an IME event 
when text is deleted, in turn hiding the insertion handle.

BUG=389444

Review URL: https://codereview.chromium.org/351403002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281686 0039d316-1c4b-4281-b951-d872f2087c98

content/public/android/java/src/org/chromium/content/browser/input/ImeAdapter.java

@@ -406,6 +406,7 @@ public class ImeAdapter {
      * @return Whether the native counterpart of ImeAdapter received the call.
      */
     boolean deleteSurroundingText(int beforeLength, int afterLength) {
+        mViewEmbedder.onImeEvent(false);
         if (mNativeImeAdapterAndroid == 0) return false;
         // Can't send the deletion key code yet because it will delete an extra char at the end.
         // Also the deleteSurroundingText message is not always ordered properly with key event