Added saftey for ensuring callback is called

Summary:
Adds a return value to `MessageQueueThread#runOnQueue`, it's implementors and one caller.

It is currently possible for a callback to not be called (because the HandlerThread has been shutdown). If the callback is mission-critical (frees resources, releases a lock, etc) the callee has no indication that it needs to do something.

This surfaces that information to the callee.

Changelog:
[Android][Changed] - Made `MessageQueueThread#runOnQueue` return a boolean. Made `MessageQueueThreadImpl#runOnQueue` return false when the runnable is not submitted.

Reviewed By: RSNara

Differential Revision: D33075516

fbshipit-source-id: bd214a39ae066c0e7d413f2eaaaa05bd072ead2a

ReactAndroid/src/main/java/com/facebook/react/bridge/ReactContext.java

@@ -396,8 +396,8 @@ public class ReactContext extends ContextWrapper {
     return Assertions.assertNotNull(mJSMessageQueueThread).isOnThread();
   }
 
-  public void runOnJSQueueThread(Runnable runnable) {
-    Assertions.assertNotNull(mJSMessageQueueThread).runOnQueue(runnable);
+  public boolean runOnJSQueueThread(Runnable runnable) {
+    return Assertions.assertNotNull(mJSMessageQueueThread).runOnQueue(runnable);
   }
 
   /**

ReactAndroid/src/main/java/com/facebook/react/bridge/queue/MessageQueueThread.java

@@ -19,7 +19,7 @@ public interface MessageQueueThread {
    * if it is being submitted from the same queue Thread.
    */
   @DoNotStrip
-  void runOnQueue(Runnable runnable);
+  boolean runOnQueue(Runnable runnable);
 
   /**
    * Runs the given Callable on this Thread. It will be submitted to the end of the event queue even

ReactAndroid/src/main/java/com/facebook/react/bridge/queue/MessageQueueThreadImpl.java

@@ -55,15 +55,17 @@ public class MessageQueueThreadImpl implements MessageQueueThread {
    */
   @DoNotStrip
   @Override
-  public void runOnQueue(Runnable runnable) {
+  public boolean runOnQueue(Runnable runnable) {
     if (mIsFinished) {
       FLog.w(
           ReactConstants.TAG,
           "Tried to enqueue runnable on already finished thread: '"
               + getName()
               + "... dropping Runnable.");
+      return false;
     }
     mHandler.post(runnable);
+    return true;
   }
 
   @DoNotStrip