[Chromecast] Clarify lifetime of CastGinRunner.

chromecast/renderer/cast_gin_runner.cc

 // 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.
 
 #include "chromecast/renderer/cast_gin_runner.h"
 
 #include "content/public/renderer/render_frame.h"
 #include "gin/per_context_data.h"
 #include "third_party/WebKit/public/web/WebFrame.h"
+#include "third_party/WebKit/public/web/WebKit.h"
 #include "third_party/WebKit/public/web/WebLocalFrame.h"
 #include "third_party/WebKit/public/web/WebScriptSource.h"
 
 namespace chromecast {
 namespace shell {
 
-CastGinRunner::CastGinRunner(content::RenderFrame* render_frame)
-    : content::RenderFrameObserver(render_frame),
-      frame_(render_frame->GetWebFrame()),
-      context_holder_(
-          gin::PerContextData::From(frame_->mainWorldScriptContext())
-              ->context_holder()) {
+namespace {
+const void* kCastContextData;
+const void* kCastGinRunnerKey = static_cast<const void*>(&kCastContextData);

[slan, 2016/12/01 01:33:22]

nit: Could you add a comment explaining that the key value must be a memory
address that is unique outside this file, but shared among all created instances
of CastGinRunner?

[slan, 2016/12/01 01:37:51]

Alternatively, you could also key on |render_frame| or the associated WebFrame*.
This would be an allocated address (and therefore unique) for the lifetime of
the CastGinRunner. And it would eliminate the need for this trick.

+}
+
+// static
+CastGinRunner* CastGinRunner::Get(content::RenderFrame* render_frame) {
+  DCHECK(render_frame);
+  blink::WebFrame* frame = render_frame->GetWebFrame();
+  v8::HandleScope handle_scope(blink::mainThreadIsolate());
+  gin::PerContextData* context_data =
+      gin::PerContextData::From(frame->mainWorldScriptContext());
+  CastGinRunner* runner =
+      static_cast<CastGinRunner*>(context_data->GetUserData(kCastGinRunnerKey));
+  return runner ? runner : new CastGinRunner(frame, context_data);
+}
+
+CastGinRunner::CastGinRunner(blink::WebFrame* frame,
+                             gin::PerContextData* context_data)
+    : frame_(frame), context_holder_(context_data->context_holder()) {
   DCHECK(frame_);
   DCHECK(context_holder_);
-  gin::PerContextData* context_data =
-      gin::PerContextData::From(frame_->mainWorldScriptContext());
 
-  v8::Isolate::Scope isolate_scope(context_holder_->isolate());
-  v8::HandleScope handle_scope(context_holder_->isolate());
-
-  context_data->SetUserData(kCastContextData, this);
+  // context_data takes ownership of this class.
+  context_data->SetUserData(kCastGinRunnerKey, this);
 
   // Note: this installs the runner globally. If we need to support more than
   // one runner at a time we'll have to revisit this.
   context_data->set_runner(this);
 }
 
-CastGinRunner::~CastGinRunner() {
-  RemoveUserData(render_frame()->GetWebFrame()->mainWorldScriptContext());
-}
+CastGinRunner::~CastGinRunner() {}
 
 void CastGinRunner::Run(const std::string& source,
                         const std::string& resource_name) {
   frame_->executeScript(
       blink::WebScriptSource(blink::WebString::fromUTF8(source)));
 }
 
 v8::Local<v8::Value> CastGinRunner::Call(v8::Local<v8::Function> function,
                                          v8::Local<v8::Value> receiver,
                                          int argc,
                                          v8::Local<v8::Value> argv[]) {
   return frame_->callFunctionEvenIfScriptDisabled(function, receiver, argc,
                                                   argv);
 }
 
 gin::ContextHolder* CastGinRunner::GetContextHolder() {
   return context_holder_;
 }
 
-void CastGinRunner::WillReleaseScriptContext(v8::Local<v8::Context> context,
-                                             int world_id) {
-  RemoveUserDataFromMainWorldContext();
-}
-
-void CastGinRunner::DidClearWindowObject() {
-  RemoveUserDataFromMainWorldContext();
-}
-
-void CastGinRunner::OnDestruct() {
-  RemoveUserDataFromMainWorldContext();
-}
-
-void CastGinRunner::RemoveUserDataFromMainWorldContext() {
-  v8::HandleScope handle_scope(context_holder_->isolate());
-  RemoveUserData(render_frame()->GetWebFrame()->mainWorldScriptContext());
-}
-
-void CastGinRunner::RemoveUserData(v8::Local<v8::Context> context) {
-  gin::PerContextData* context_data = gin::PerContextData::From(context);
-  if (!context_data)
-    return;
-
-  context_data->RemoveUserData(kCastContextData);
-}
-
 }  // namespace shell
 }  // namespace chromecast