Add CWVUserContentController which enables injecting JavaScripts.

ios/web_view/internal/cwv_web_view_configuration.mm

 // Copyright 2017 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/public/cwv_web_view_configuration.h"
 #import "ios/web_view/internal/cwv_web_view_configuration_internal.h"
 
+#import "ios/web_view/internal/cwv_user_content_controller_internal.h"
 #import "ios/web_view/internal/web_view_browser_state.h"
 #import "ios/web_view/internal/web_view_web_client.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @interface CWVWebViewConfiguration ()
 // Initialize configuration with the specified browser state.
 - (instancetype)initWithBrowserState:
     (ios_web_view::WebViewBrowserState*)browserState;
 @end
 
 @implementation CWVWebViewConfiguration {
   // TODO(crbug.com/690182): CWVWebViewConfiguration should own _browserState.
   ios_web_view::WebViewBrowserState* _browserState;
 }
 
+@synthesize userContentController = _userContentController;
+
 + (instancetype)defaultConfiguration {
   static dispatch_once_t once;
   static CWVWebViewConfiguration* configuration;
   dispatch_once(&once, ^{
     ios_web_view::WebViewWebClient* client =
         static_cast<ios_web_view::WebViewWebClient*>(web::GetWebClient());
     configuration = [[self alloc] initWithBrowserState:client->browser_state()];
   });
   return configuration;
 }
 
 + (instancetype)incognitoConfiguration {
   static dispatch_once_t once;
   static CWVWebViewConfiguration* configuration;
   dispatch_once(&once, ^{
     ios_web_view::WebViewWebClient* client =
         static_cast<ios_web_view::WebViewWebClient*>(web::GetWebClient());
     configuration = [[self alloc]
         initWithBrowserState:client->off_the_record_browser_state()];
   });
   return configuration;
 }
 
 - (instancetype)initWithBrowserState:
     (ios_web_view::WebViewBrowserState*)browserState {
   self = [super init];
   if (self) {
     _browserState = browserState;
+    _userContentController =
+        [[CWVUserContentController alloc] initWithConfiguration:self];
   }
   return self;
 }
 
 - (BOOL)isPersistent {
   return !_browserState->IsOffTheRecord();
 }
 
 - (ios_web_view::WebViewBrowserState*)browserState {
   return _browserState;
 }
 
 // NSCopying
 
 - (id)copyWithZone:(NSZone*)zone {
   return [[[self class] allocWithZone:zone] initWithBrowserState:_browserState];
 }
 
 @end