Move ExecuteScript method from WebFrame to WebLocalFrame.

components/plugins/renderer/loadable_plugin_placeholder.cc

Index: components/plugins/renderer/loadable_plugin_placeholder.cc
diff --git a/components/plugins/renderer/loadable_plugin_placeholder.cc b/components/plugins/renderer/loadable_plugin_placeholder.cc
index 576786453687c1f4fb6a4b98eb2a147a70cdd991..32a13e6771a939e930459c7c4f464072126b8148 100644
--- a/components/plugins/renderer/loadable_plugin_placeholder.cc
+++ b/components/plugins/renderer/loadable_plugin_placeholder.cc
@@ -145,7 +145,12 @@ void LoadablePluginPlaceholder::UpdateMessage() {
     return;
   std::string script =
       "window.setMessage(" + base::GetQuotedJSONString(message_) + ")";
-  plugin()->web_view()->MainFrame()->ExecuteScript(
+  blink::WebFrame* main_frame = plugin()->web_view()->MainFrame();
+  if (!main_frame->IsWebLocalFrame()) {

[dcheng, 2017/06/04 10:37:22]

As this is a WebViewPlugin, which is only used to load very simple content for
the plugin placeholder, we should be able to just
DCHECK(main_frame->IsWebLocalFrame()) here.

(One possibility to make this clear is to directly expose a main_frame() helper
on WebViewPlugin that does the casting internally)

[Łukasz Anforowicz, 2017/06/05 17:10:57]

Good point - done:

- I've exposed WebViewPlugin::main_frame accessor that returns a local frame. 
This means that WebViewPlugin::web_view accessor can be made private.

- I've changed a few places to use the main_frame accessor, rather than call
ToWebLocalFrame, etc.

+    NOTREACHED();
+    return;
+  }
+  main_frame->ToWebLocalFrame()->ExecuteScript(
       blink::WebScriptSource(blink::WebString::FromUTF8(script)));
 }
 
@@ -252,7 +257,12 @@ void LoadablePluginPlaceholder::OnUnobscuredRectUpdate(
     std::string script = base::StringPrintf(
         "window.resizePoster('%dpx', '%dpx', '%dpx', '%dpx')", x, y, width,
         height);
-    plugin()->web_view()->MainFrame()->ExecuteScript(
+    blink::WebFrame* main_frame = plugin()->web_view()->MainFrame();
+    if (!main_frame->IsWebLocalFrame()) {
+      NOTREACHED();
+      return;
+    }
+    main_frame->ToWebLocalFrame()->ExecuteScript(
         blink::WebScriptSource(blink::WebString::FromUTF8(script)));
   }
 }