Pepper: Move FileRef to the "new" resource proxy.

content/public/renderer/renderer_ppapi_host.h

Index: content/public/renderer/renderer_ppapi_host.h
diff --git a/content/public/renderer/renderer_ppapi_host.h b/content/public/renderer/renderer_ppapi_host.h
index 1275429a132feefe7d4fe06bec774d9e9908a728..88a863fd2d72d6313fdc517d34a223cd0291caf2 100644
--- a/content/public/renderer/renderer_ppapi_host.h
+++ b/content/public/renderer/renderer_ppapi_host.h
@@ -49,6 +49,11 @@ class RendererPpapiHost {
  public:
   // Returns the RendererPpapiHost associated with the given PP_Instance,
   // or NULL if the instance is invalid.
+  //
+  // Do NOT use this when dealing with an "external plugin" that serves as a
+  // bootstrap to load a second plugin. This is because the two will share a
+  // PP_Instance, and the RendererPpapiHost* for the second plugin will be
+  // returned after we switch the proxy on.
   CONTENT_EXPORT static RendererPpapiHost* GetForPPInstance(
       PP_Instance instance);