libmojo: Uprev the library to r456626 from Chromium

Pulled the latest and greatest version of libmojo from Chromium.

The merge was done against r456626 which corresponds to git commit
08266b3fca707804065a2cfd60331722ade41969 of Mar 14, 2017

Notable changes are:
- generated binding files are now split in 2 files, interface.mojom.h
  and interface.mojom-shared.h

Change-Id: Idcfd27310e2c9d3c452b671c7ff7a755c3963618
diff --git a/base/android/java_handler_thread.h b/base/android/java_handler_thread.h
index 1709ff4..96f2f0a 100644
--- a/base/android/java_handler_thread.h
+++ b/base/android/java_handler_thread.h
@@ -14,7 +14,6 @@
 namespace base {
 
 class MessageLoop;
-class WaitableEvent;
 
 namespace android {
 
@@ -41,10 +40,15 @@
                   const JavaParamRef<jobject>& obj,
                   jlong event);
 
+  virtual void StartMessageLoop();
+  virtual void StopMessageLoop();
+
   static bool RegisterBindings(JNIEnv* env);
 
- private:
+ protected:
   std::unique_ptr<base::MessageLoop> message_loop_;
+
+ private:
   ScopedJavaGlobalRef<jobject> java_thread_;
 };