Add CWVUserContentController which enables injecting JavaScripts.

ios/web_view/internal/web_view_web_client.mm

 // Copyright 2014 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.
 
 #import "ios/web_view/internal/web_view_web_client.h"
 
 #include "base/strings/sys_string_conversions.h"
 #include "ios/web/public/user_agent.h"
 #include "ios/web_view/internal/web_view_browser_state.h"
+#import "ios/web_view/internal/web_view_early_page_script_provider.h"
 #import "ios/web_view/internal/web_view_web_main_parts.h"
 #import "ios/web_view/public/cwv_delegate.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 namespace ios_web_view {
 
 WebViewWebClient::WebViewWebClient(id<CWVDelegate> delegate)
@@ skipping 15 matching lines @@
 }
 
 std::string WebViewWebClient::GetProduct() const {
   return base::SysNSStringToUTF8([delegate_ partialUserAgent]);
 }
 
 std::string WebViewWebClient::GetUserAgent(web::UserAgentType type) const {
   return web::BuildUserAgentFromProduct(GetProduct());
 }
 
+NSString* WebViewWebClient::GetEarlyPageScript(
+    web::BrowserState* browser_state) const {
+  return WebViewEarlyPageScriptProvider::FromBrowserState(browser_state)
+      .GetScript();
+}
+
 }  // namespace ios_web_view