[ios] Adds a provider API for AudioSessionController.

ios/public/provider/chrome/browser/chrome_browser_provider.h

Index: ios/public/provider/chrome/browser/chrome_browser_provider.h
diff --git a/ios/public/provider/chrome/browser/chrome_browser_provider.h b/ios/public/provider/chrome/browser/chrome_browser_provider.h
index 599c59183844617d0c3f352a9c8f55fe93ab79be..ef57773fa2eed8a436a170b88f71268ca7d84566 100644
--- a/ios/public/provider/chrome/browser/chrome_browser_provider.h
+++ b/ios/public/provider/chrome/browser/chrome_browser_provider.h
@@ -22,6 +22,7 @@ class GURL;
 class InfoBarViewDelegate;
 class PrefRegistrySimple;
 class PrefService;
+class VoiceSearchProvider;
 
 namespace autofill {
 class CardUnmaskPromptController;
@@ -141,8 +142,12 @@ class ChromeBrowserProvider {
   virtual bool IsSafeBrowsingEnabled(const base::Closure& on_update_callback);
 
   // Returns the list of available voice search languages.
+  // TODO(rohitrao): Remove once callers are going through VoiceSearchProvider.
   virtual NSArray* GetAvailableVoiceSearchLanguages() const;
 
+  // Returns an instance of the voice search provider, if one exists.
+  virtual VoiceSearchProvider* GetVoiceSearchProvider() const;
+
   // Returns the SyncedWindowDelegatesGetter implementation.
   virtual std::unique_ptr<sync_sessions::SyncedWindowDelegatesGetter>
   CreateSyncedWindowDelegatesGetter(ios::ChromeBrowserState* browser_state);