Add CWVUserContentController which enables injecting JavaScripts.

ios/web_view/internal/web_view_early_page_script_provider.h

Index: ios/web_view/internal/web_view_early_page_script_provider.h
diff --git a/ios/web_view/internal/web_view_early_page_script_provider.h b/ios/web_view/internal/web_view_early_page_script_provider.h
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+++ b/ios/web_view/internal/web_view_early_page_script_provider.h
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+// 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.
+
+#ifndef IOS_WEB_VIEW_INTERNAL_WEB_VIEW_EARLY_PAGE_SCRIPT_PROVIDER_H_
+#define IOS_WEB_VIEW_INTERNAL_WEB_VIEW_EARLY_PAGE_SCRIPT_PROVIDER_H_
+
+#include <Foundation/Foundation.h>
+
+#include "base/mac/scoped_nsobject.h"
+#include "base/macros.h"
+#include "base/supports_user_data.h"
+
+namespace web {
+class BrowserState;
+}
+
+namespace ios_web_view {
+
+// A provider class associated with a single web::BrowserState object. Keeps
+// an early page script, a JavaScript injected into all pages as early as
+// possible.
+//
+// Not threadsafe. Must be used only on the main thread.
+class WebViewEarlyPageScriptProvider : public base::SupportsUserData::Data {
+ public:
+  ~WebViewEarlyPageScriptProvider() override;
+
+  // Returns a provider for the given |browser_state|. Lazily attaches one if it
+  // does not exist. |browser_state| can not be null.
+  static WebViewEarlyPageScriptProvider& FromBrowserState(
+      web::BrowserState* _Nonnull browser_state);
+
+  // Getter and Setter for the JavaScript source code.
+  NSString* _Nonnull GetScript() { return script_.get(); }
+  void SetScript(NSString* _Nonnull script);
+
+ private:
+  WebViewEarlyPageScriptProvider();
+
+  // The JavaScript source code.
+  base::scoped_nsobject<NSString> script_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebViewEarlyPageScriptProvider);
+};
+
+}  // namespace ios_web_view
+
+#endif  // IOS_WEB_VIEW_INTERNAL_WEB_VIEW_EARLY_PAGE_SCRIPT_PROVIDER_H_