Add tracing to when SO libraries are loaded

Summary:
Currently, loading SO libraries is pretty expensive. While they are triggered due to accessing `ReadableNativeArray`. However, with preloader experiments, this block seems to move around and is loaded when the first dependent class loads it.

Also, as a part of D10108380, this will be moved again.

Adding a trace to keep track of where it moves.

Reviewed By: achen1

Differential Revision: D9890280

fbshipit-source-id: 4b331ef1d7e824935bf3708442537349d2d631d0

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

@@ -7,16 +7,21 @@
 
 package com.facebook.react.bridge;
 
+import static com.facebook.systrace.Systrace.TRACE_TAG_REACT_JAVA_BRIDGE;
+
 import com.facebook.soloader.SoLoader;
+import com.facebook.systrace.Systrace;
 
 public class ReactBridge {
   private static boolean sDidInit = false;
   public static void staticInit() {
     // No locking required here, worst case we'll call into SoLoader twice
     // which will do its own locking internally
     if (!sDidInit) {
+      Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "ReactBridge.staticInit::load:reactnativejni");
       SoLoader.loadLibrary("reactnativejni");
       sDidInit = true;
+      Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
     }
   }
 }