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
new file mode 100644
index 0000000000000000000000000000000000000000..97d34e64f926fc56e535587ffed34cfb6e14628c
--- /dev/null
+++ b/ios/web_view/internal/web_view_early_page_script_provider.h
@@ -0,0 +1,48 @@
+// 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/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* browser_state);
+
+  // Getter and Setter for the JavaScript source code.
+  NSString* GetScript() { return script_; }
+  void SetScript(NSString* script) { script_ = script; }

[michaeldo, 2017/03/21 16:12:34]

Please document setter as script must be nonnull. This is documented as a
requirement in web::WebClient on the GetEarlyPageScript method. 

[Eugene But (OOO till 7-30), 2017/03/21 16:47:55]

 script_ = [script copy];

[Hiroshi Ichikawa, 2017/03/22 04:52:52]

Done.

[Hiroshi Ichikawa, 2017/03/22 04:52:52]

I *documented* the requirement by adding _Nonnull annotation. Is it OK, to use
_Nonnull annontation in Objective-C++ code?

[michaeldo, 2017/03/22 23:03:32]

I found at least one other reference to _Nonnull so yes I think it is OK to use
in terms of use in the repo. In terms of use in general, it looks like it is a
compiler feature, here is a little more info:
http://stackoverflow.com/questions/40892529/nullability-rules-for-c-objects-i...

[Hiroshi Ichikawa, 2017/03/23 02:48:05]

Acknowledged.

+
+ private:
+  WebViewEarlyPageScriptProvider();

[michaeldo, 2017/03/21 16:12:34]

please move to immediately after public: above

[Hiroshi Ichikawa, 2017/03/22 04:52:52]

Shouldn't the constructor be private so that it can be only instantiated via
FromBrowserState()? I followed this class as an example:
https://cs.chromium.org/chromium/src/ios/web/web_state/ui/wk_web_view_configu...
which also declares the constructor as private.

[Eugene But (OOO till 7-30), 2017/03/22 15:08:50]

Private constructor seems like a better choice

[michaeldo, 2017/03/22 23:03:32]

Sorry, you're right. I didn't see why it was private, but yes. It makes sense
because it is created by FromBrowserState().

+
+  // The JavaScript source code.
+  NSString* script_;

[michaeldo, 2017/03/21 16:12:34]

Please use:

base::scoped_nsobject<NSString> script_

and update setter above to use script_.reset(script)

[Hiroshi Ichikawa, 2017/03/22 04:52:52]

Done. What is the benefit using scoped_nsobject compared to a raw pointer? I
believe raw pointers are also reference-counted under ARC.

[michaeldo, 2017/03/22 23:03:32]

I mostly suggested based on style and consistency. There may be other benefits,
but I'm not sure of them all. However, these are good questions for
Chromium-dev. I'm sure many people there would have deeper knowledge of all
these types of things and could identify improvements/cleanups. Or at least
suggest a modification to the comments within scoped_nsobject.h to be more
explicit about some of this items with relation to newer compiler features like
ARC.

[Hiroshi Ichikawa, 2017/03/23 02:48:05]

Acknowledged.

+
+  DISALLOW_COPY_AND_ASSIGN(WebViewEarlyPageScriptProvider);
+};
+
+}  // namespace ios_web_view
+
+#endif  // IOS_WEB_VIEW_INTERNAL_WEB_VIEW_EARLY_PAGE_SCRIPT_PROVIDER_H_