Refactor FabricSoLoader to ensure sDidInit is accessed correctly

Summary:
sDidInit can be accessed from different threads, this diff refactors the definition of this variable to be volatile and also to be assigned at the end of the staticInit() method.

Changelog:
Ensure proper initialization of FabricSoLoder

Reviewed By: ejanzer

Differential Revision: D18010919

fbshipit-source-id: 3ec7b19fdc15056b90fc01281b8c3888e93a7dd3

ReactAndroid/src/main/java/com/facebook/react/fabric/FabricSoLoader.java

@@ -15,19 +15,18 @@
 import com.facebook.systrace.Systrace;
 
 public class FabricSoLoader {
-  private static boolean sDidInit = false;
+  private static volatile boolean sDidInit = false;
 
   public static void staticInit() {
     if (sDidInit) {
       return;
     }
-    sDidInit = true;
-
     Systrace.beginSection(
         Systrace.TRACE_TAG_REACT_JAVA_BRIDGE, "FabricSoLoader.staticInit::load:fabricjni");
     ReactMarker.logMarker(ReactMarkerConstants.LOAD_REACT_NATIVE_SO_FILE_START);
     SoLoader.loadLibrary("fabricjni");
     ReactMarker.logMarker(ReactMarkerConstants.LOAD_REACT_NATIVE_SO_FILE_END);
     Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
+    sDidInit = true;
   }
 }