[Chromecast] Clarify lifetime of CastGinRunner.

chromecast/renderer/cast_gin_runner.h

 // Copyright 2016 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 CHROMECAST_RENDERER_CAST_GIN_RUNNER_H_
 #define CHROMECAST_RENDERER_CAST_GIN_RUNNER_H_
 
 #include "base/macros.h"
 #include "base/supports_user_data.h"
-#include "content/public/renderer/render_frame_observer.h"
 #include "gin/runner.h"
 
-namespace {
-const char kCastContextData[] = "CastContextData";
-}
-
 namespace blink {
 class WebFrame;
 }
 
+namespace content {
+class RenderFrame;
+}
+
+namespace gin {
+class PerContextData;
+}
+
 namespace chromecast {
 namespace shell {
 
 // Implementation of gin::Runner that forwards Runner functions to WebFrame.
-class CastGinRunner : public gin::Runner,
-                      public base::SupportsUserData::Data,
-                      public content::RenderFrameObserver {
+// This class is lazily created per RenderFrame with the Get function and it's
+// lifetime is managed by the gin::PerContextData associated with the frame.
+class CastGinRunner : public gin::Runner, public base::SupportsUserData::Data {
  public:
-  // Does not take ownership of ContextHolder.
-  CastGinRunner(content::RenderFrame* render_frame);
+  // Gets or creates the CastGinRunner for this RenderFrame
+  static CastGinRunner* Get(content::RenderFrame* render_frame);
   ~CastGinRunner() override;
 
   // gin:Runner implementation:
   void Run(const std::string& source,
            const std::string& resource_name) override;
   v8::Local<v8::Value> Call(v8::Local<v8::Function> function,
                             v8::Local<v8::Value> receiver,
                             int argc,
                             v8::Local<v8::Value> argv[]) override;
   gin::ContextHolder* GetContextHolder() override;
 
-  // content::RenderFrameObserver implementation:
-  void WillReleaseScriptContext(v8::Local<v8::Context> context,
-                                int world_id) override;
-  void DidClearWindowObject() override;
-  void OnDestruct() override;
-
  private:
-  void RemoveUserDataFromMainWorldContext();
-  void RemoveUserData(v8::Local<v8::Context> context);
+  CastGinRunner(blink::WebFrame* frame, gin::PerContextData* context_data);
 
   // Frame to execute script in.
   blink::WebFrame* const frame_;
 
   // Created by blink bindings to V8.
   gin::ContextHolder* const context_holder_;
 
   DISALLOW_COPY_AND_ASSIGN(CastGinRunner);
 };
 
 }  // namespace shell
 }  // namespace chromecast
 
 #endif  // CHROMECAST_RENDERER_CAST_GIN_RUNNER_H_