Make NativeModules immediately initializable

Summary:
## Problem:
NativeModules can only be initialized after we mark them initializable on the NativeModules thread. This work is scheduled in ReactInstanceManager.setupReactContext(), after we schedule the execution of the JS bundle on the JavaScript thread in ReactInstanceManager.createReactContext():

https://www.internalfb.com/intern/diffusion/FBS/browse/master/xplat/js/react-native-github/ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java?commit=9b58f58b8eb12281567b8d24d6d000e868e61a1f&lines=1256-1257%2C1331%2C1334-1335%2C1333-1334

So, if the timings don't work out, the JavaScript thread could start executing the JS bundle before the NativeModule thread makes all NativeModules initializable. In this case, those NativeModule will just appear to be null in C++/JavaScript.

## Fix
This diff makes all NativeModules initializable immediately after  their ModuleHolder is created. ModuleHolder.markInitializable() simply initializes initializes modules that were eagerly created.

Changelog: [Android][Fixed] - Make NativeModules immediately initializable

Reviewed By: JoshuaGross

Differential Revision: D26233372

fbshipit-source-id: a9223ff093da5b80781169be88e6ec9516c7a29b

Author: RSNara

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

@@ -50,7 +50,6 @@ public class ModuleHolder {
   private @Nullable @GuardedBy("this") NativeModule mModule;
 
   // These are used to communicate phases of creation and initialization across threads
-  private @GuardedBy("this") boolean mInitializable;
   private @GuardedBy("this") boolean mIsCreating;
   private @GuardedBy("this") boolean mIsInitializing;
 
@@ -89,7 +88,6 @@ public ModuleHolder(NativeModule nativeModule) {
     boolean shouldInitializeNow = false;
     NativeModule module = null;
     synchronized (this) {
-      mInitializable = true;
       if (mModule != null) {
         Assertions.assertCondition(!mIsInitializing);
         shouldInitializeNow = true;
@@ -193,7 +191,7 @@ private NativeModule create() {
       boolean shouldInitializeNow = false;
       synchronized (this) {
         mModule = module;
-        if (mInitializable && !mIsInitializing) {
+        if (!mIsInitializing) {
           shouldInitializeNow = true;
         }
       }
@@ -227,7 +225,7 @@ private void doInitialize(NativeModule module) {
       boolean shouldInitialize = false;
       // Check to see if another thread is initializing the object, if not claim the responsibility
       synchronized (this) {
-        if (mInitializable && !mIsInitializing) {
+        if (!mIsInitializing) {
           shouldInitialize = true;
           mIsInitializing = true;
         }