RN: Simplify Context Creation (Android)

Summary:
Every call site is either already using `createReactContextInBackground` correctly or guarding the invocation using `hasStartedCreatingInitialContext`. This is an unnecessary and overly complex dance that can be simplified.

This revision simplifies the use of `createReactContextInBackground` by integrating the check. This is not a breaking change.

Reviewed By: zackargyle, mdvacca

Differential Revision: D15566632

fbshipit-source-id: 7b50285c9ac6776d1297d2c9c53dff208851b722

ReactAndroid/src/main/java/com/facebook/react/HeadlessJsTaskService.java

@@ -108,9 +108,7 @@ public abstract class HeadlessJsTaskService extends Service implements HeadlessJ
             reactInstanceManager.removeReactInstanceEventListener(this);
           }
         });
-      if (!reactInstanceManager.hasStartedCreatingInitialContext()) {
-        reactInstanceManager.createReactContextInBackground();
-      }
+      reactInstanceManager.createReactContextInBackground();
     } else {
       invokeStartTask(reactContext, taskConfig);
     }

ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java

@@ -325,23 +325,17 @@ public class ReactInstanceManager {
   /**
    * Trigger react context initialization asynchronously in a background async task. This enables
    * applications to pre-load the application JS, and execute global code before
-   * {@link ReactRootView} is available and measured. This should only be called the first time the
-   * application is set up, which is enforced to keep developers from accidentally creating their
-   * application multiple times without realizing it.
+   * {@link ReactRootView} is available and measured.
    *
    * Called from UI thread.
    */
   @ThreadConfined(UI)
   public void createReactContextInBackground() {
     Log.d(ReactConstants.TAG, "ReactInstanceManager.createReactContextInBackground()");
-    Assertions.assertCondition(
-        !mHasStartedCreatingInitialContext,
-        "createReactContextInBackground should only be called when creating the react " +
-            "application for the first time. When reloading JS, e.g. from a new file, explicitly" +
-            "use recreateReactContextInBackground");
-
-    mHasStartedCreatingInitialContext = true;
-    recreateReactContextInBackgroundInner();
+    if (!mHasStartedCreatingInitialContext) {
+      mHasStartedCreatingInitialContext = true;
+      recreateReactContextInBackgroundInner();
+    }
   }
 
   /**

ReactAndroid/src/main/java/com/facebook/react/ReactRootView.java

@@ -394,9 +394,7 @@ public class ReactRootView extends FrameLayout implements RootView, ReactRoot {
         // TODO initialize surface here
       }
 
-      if (!mReactInstanceManager.hasStartedCreatingInitialContext()) {
-        mReactInstanceManager.createReactContextInBackground();
-      }
+      mReactInstanceManager.createReactContextInBackground();
 
       attachToReactInstanceManager();