Add new NTP layout with snippet cards and hide it behind a flag

chrome/browser/android/ntp/ntp_snippets_bridge.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_ANDROID_NTP_NTP_SNIPPETS_BRIDGE_H_
 #define CHROME_BROWSER_ANDROID_NTP_NTP_SNIPPETS_BRIDGE_H_
 
 #include <jni.h>
 
 #include "base/android/scoped_java_ref.h"
 #include "base/scoped_observer.h"
 #include "components/ntp_snippets/ntp_snippets_service.h"
 
-// The C++ counterpart to NTPSnippetsBridge.java. Enables Java code to access
+// The C++ counterpart to SnippetsBridge.java. Enables Java code to access
 // the list of snippets to show on the NTP
 class NTPSnippetsBridge : public ntp_snippets::NTPSnippetsServiceObserver {
  public:
   NTPSnippetsBridge(JNIEnv* env,
                     const base::android::JavaParamRef<jobject>& j_profile);
   void Destroy(JNIEnv* env, const base::android::JavaParamRef<jobject>& obj);
 
   void SetObserver(JNIEnv* env,
                    const base::android::JavaParamRef<jobject>& obj,
                    const base::android::JavaParamRef<jobject>& j_observer);
 
   static bool Register(JNIEnv* env);
 
  private:
   ~NTPSnippetsBridge() override;
 
   // NTPSnippetsServiceObserver overrides
   void NTPSnippetsServiceLoaded(
       ntp_snippets::NTPSnippetsService* service) override;
   void NTPSnippetsServiceShutdown(
       ntp_snippets::NTPSnippetsService* service) override;
 
   ntp_snippets::NTPSnippetsService* ntp_snippets_service_;
 
+  // Used to notify the Java side when new snippets have been fetched.
   base::android::ScopedJavaGlobalRef<jobject> observer_;
   ScopedObserver<ntp_snippets::NTPSnippetsService,
                  ntp_snippets::NTPSnippetsServiceObserver>
       snippet_service_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsBridge);
 };
 
 #endif  // CHROME_BROWSER_ANDROID_NTP_NTP_SNIPPETS_BRIDGE_H_