Add CWVUserContentController which enables injecting JavaScripts.

ios/web_view/internal/web_view_early_page_script_provider.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/internal/web_view_early_page_script_provider.h"
+
+#import <Foundation/Foundation.h>
+
+#include "ios/web/public/browser_state.h"
+#include "ios/web/public/web_thread.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace ios_web_view {
+
+namespace {
+// A key used to associate a WebViewEarlyPageScriptProvider with a BrowserState.
+const char kWebViewEarlyPageScriptProviderKeyName[] =
+    "web_view_early_page_script_provider";
+
+}  // namespace
+
+// static
+WebViewEarlyPageScriptProvider&
+WebViewEarlyPageScriptProvider::FromBrowserState(
+    web::BrowserState* _Nonnull browser_state) {
+  DCHECK_CURRENTLY_ON(web::WebThread::UI);
+  DCHECK(browser_state);
+  if (!browser_state->GetUserData(kWebViewEarlyPageScriptProviderKeyName)) {
+    browser_state->SetUserData(kWebViewEarlyPageScriptProviderKeyName,
+                               std::unique_ptr<WebViewEarlyPageScriptProvider>(
+                                   new WebViewEarlyPageScriptProvider()));
+  }
+  return *(static_cast<WebViewEarlyPageScriptProvider*>(
+      browser_state->GetUserData(kWebViewEarlyPageScriptProviderKeyName)));
+}
+
+WebViewEarlyPageScriptProvider::~WebViewEarlyPageScriptProvider() = default;
+
+void WebViewEarlyPageScriptProvider::SetScript(NSString* _Nonnull script) {
+  script_.reset((NSString * _Nonnull)[script copy]);

[michaeldo, 2017/03/22 23:03:33]

Is this cast needed? I would expect this to be OK:
script_.reset([script copy]);

[Hiroshi Ichikawa, 2017/03/23 02:18:40]

It worked, thanks. Done.

+}
+
+WebViewEarlyPageScriptProvider::WebViewEarlyPageScriptProvider()
+    : script_([[NSString alloc] init]) {}
+
+}  // namespace ios_web_view