Don't emit dimensions update event on initial load

Summary: On iOS we don't emit the didUpdateDimensions event in JS when the first React Native screen is rendered, so let's keep the behavior the same on Android.

Reviewed By: mdvacca

Differential Revision: D19506829

fbshipit-source-id: d0122d18be79177318c3f059ed396f990eeabcb7

ReactAndroid/src/main/java/com/facebook/react/modules/deviceinfo/DeviceInfoModule.java

@@ -89,7 +89,9 @@ public void emitUpdateDimensionsEvent() {
       // Don't emit an event to JS if the dimensions haven't changed
       WritableNativeMap displayMetrics =
           DisplayMetricsHolder.getDisplayMetricsNativeMap(mFontScale);
-      if (!displayMetrics.equals(mPreviousDisplayMetrics)) {
+      if (mPreviousDisplayMetrics == null) {
+        mPreviousDisplayMetrics = displayMetrics.copy();
+      } else if (!displayMetrics.equals(mPreviousDisplayMetrics)) {
         mPreviousDisplayMetrics = displayMetrics.copy();
         mReactApplicationContext
             .getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)