[ios] Adds VoiceSearchProvider::IsVoiceSearchEnabled().

ios/public/provider/chrome/browser/voice/voice_search_provider.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 IOS_PUBLIC_PROVIDER_CHROME_BROWSER_VOICE_VOICE_SEARCH_PROVIDER_H_
 #define IOS_PUBLIC_PROVIDER_CHROME_BROWSER_VOICE_VOICE_SEARCH_PROVIDER_H_
 
 #include <Foundation/Foundation.h>
 #include <UIKit/UIKit.h>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 
 class AudioSessionController;
 @protocol VoiceSearchBar;
 class VoiceSearchController;
 
 namespace ios {
 class ChromeBrowserState;
 }
 
 // VoiceSearchProvider allows embedders to provide functionality related to
 // voice search.
 class VoiceSearchProvider {
  public:
   VoiceSearchProvider() = default;
   virtual ~VoiceSearchProvider() = default;
 
+  // Returns true if voice search is enabled.  The other methods in this
+  // provider must not be called if this method returns false.
+  virtual bool IsVoiceSearchEnabled() const;
+
   // Returns the list of available voice search languages.
   virtual NSArray* GetAvailableLanguages() const;
 
   // Returns the singleton audio session controller.
   virtual AudioSessionController* GetAudioSessionController() const;
 
   // Creates a new VoiceSearchController object.
   virtual scoped_refptr<VoiceSearchController> CreateVoiceSearchController(
       ios::ChromeBrowserState* browser_state) const;
 
   // Creates a new VoiceSearchBar.  The caller assumes ownership.
   virtual UIView<VoiceSearchBar>* CreateVoiceSearchBar(CGRect frame) const
       NS_RETURNS_RETAINED;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(VoiceSearchProvider);
 };
 
 #endif  // IOS_PUBLIC_PROVIDER_CHROME_BROWSER_VOICE_VOICE_SEARCH_PROVIDER_H_