Prevent EML messages from reloading indefinitely

- openMessageSync for EML files touches the provider since it copies
things into the Message table from temporary attachment data. Therefore,
acting on a reload of an EML message will trigger the observer, and do
the same thing.
- still unsure when or how this regressed, but I can't see the previous
behavior being correct regardless

Bug: 5150886
Change-Id: Icfcea7beb95b0fbb026184d6fdecc93c810569ef

src/com/android/email/activity/MessageFileViewFragment.java

@@ -121,6 +121,12 @@ public class MessageFileViewFragment extends MessageViewFragmentBase {
         return msg;
     }
 
+    @Override
+    protected Message reloadMessageSync(Activity activity) {
+        // EML files will never change, so just return the same copy.
+        return getMessage();
+    }
+
     /**
      * {@inheritDoc}
      *

src/com/android/email/activity/MessageViewFragmentBase.java

@@ -1035,6 +1035,14 @@ public abstract class MessageViewFragmentBase extends Fragment implements View.O
      */
     protected abstract Message openMessageSync(Activity activity);
 
+    /**
+     * Called in a background thread to reload a new copy of the Message in case something has
+     * changed.
+     */
+    protected Message reloadMessageSync(Activity activity) {
+        return openMessageSync(activity);
+    }
+
     /**
      * Async task for loading a single message outside of the UI thread
      */
@@ -1097,7 +1105,7 @@ public abstract class MessageViewFragmentBase extends Fragment implements View.O
             if (activity == null) {
                 return null;
             } else {
-                return openMessageSync(activity);
+                return reloadMessageSync(activity);
             }
         }
 
@@ -1878,7 +1886,9 @@ public abstract class MessageViewFragmentBase extends Fragment implements View.O
 
         @Override
         public void onChange(boolean selfChange) {
-            mThrottle.onEvent();
+            if (mRegistered) {
+                mThrottle.onEvent();
+            }
         }
 
         /** This method is delay-called by {@link Throttle} on the UI thread. */