Adds methods for Cast support to ios::ChromeBrowserProvider.

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 cf8dc7ed08eb8f091c08d2e08e741d28c32d2ef2..37bf44b315557ece7c189da3be4cc674b308d249 100644
--- a/ios/public/provider/chrome/browser/chrome_browser_provider.h
+++ b/ios/public/provider/chrome/browser/chrome_browser_provider.h
@@ -32,6 +32,10 @@ namespace net {
 class URLRequestContextGetter;
 }
 
+namespace web {
+class WebState;
+}
+
 namespace sync_sessions {
 class SyncedWindowDelegatesGetter;
 }
@@ -115,6 +119,17 @@ class ChromeBrowserProvider {
   virtual UITextField<TextFieldStyling>* CreateStyledTextField(
       CGRect frame) const NS_RETURNS_RETAINED;
 
+  // Initializes the cast service.  Should be called soon after the given
+  // |tab_model| is created.
+  // TODO(rohitrao): Change from |id| to |TabModel*| once TabModel is moved into

[rohitrao (ping after 24h), 2016/10/05 20:19:56]

Thoughts on using id here instead of TabModel*?  Are there any better options?

+  // the Chromium tree.
+  virtual void InitializeCastService(id tab_model) const;
+
+  // Adds Cast Sender API support to the given |web_state|, if it is supported
+  // by this embedder.
+  virtual void AddCastAPISupportToWebState(web::WebState* web_state,
+                                           NSString* tab_id) const;

[rohitrao (ping after 24h), 2016/10/05 20:19:56]

I thought about having this API take a std::string instead, but that would
require conversions from and to NSString.  It's only once per tab though, so we
could take the hit if the API would be better with std::string.

+
   // Returns whether safe browsing is enabled. See the comment on
   // metrics_services_manager_client.h for details on |on_update_callback|.
   virtual bool IsSafeBrowsingEnabled(const base::Closure& on_update_callback);