Convert the async device ID getter to a chrome resource host

content/public/browser/browser_ppapi_host.h

Index: content/public/browser/browser_ppapi_host.h
diff --git a/content/public/browser/browser_ppapi_host.h b/content/public/browser/browser_ppapi_host.h
index aa9799071cd2460ab1fc02226121d90321348fe8..622a7fbb85516f8dda9e5c19965698b047ba2fb3 100644
--- a/content/public/browser/browser_ppapi_host.h
+++ b/content/public/browser/browser_ppapi_host.h
@@ -5,8 +5,12 @@
 #ifndef CONTENT_PUBLIC_BROWSER_BROWSER_PPAPI_HOST_H_
 #define CONTENT_PUBLIC_BROWSER_BROWSER_PPAPI_HOST_H_
 
+#include "base/callback_forward.h"
 #include "base/process.h"
 #include "content/common/content_export.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/render_view_host.h"
+#include "ppapi/c/pp_instance.h"
 
 namespace ppapi {
 namespace host {
@@ -23,14 +27,73 @@ namespace content {
 // lives entirely on the I/O thread.
 class CONTENT_EXPORT BrowserPpapiHost {
  public:
+  struct RenderViewIDs {

[jam, 2012/09/10 16:22:21]

nit: we've avoied a struct for these two so far afaik; i think it wouldn't be
consistent to use it in some places.

[brettw, 2012/09/11 20:25:20]

I insert these into a map. I can use a pair but then the review comment would be
that I should use a named struct. I could keep the struct internal to this class
and expose two out params for the GetRenderViewIDsForInstance.

+    int process_id;
+    int view_id;
+  };
+
   // Returns the PpapiHost object.
   virtual ppapi::host::PpapiHost* GetPpapiHost() = 0;
 
   // Returns the handle to the plugin process.
   virtual base::ProcessHandle GetPluginProcessHandle() const = 0;
 
+  // Returns true if the given PP_Instance is valid.
+  virtual bool IsValidInstance(PP_Instance instance) const = 0;
+
+  // Returns the process/view Ids associated with the RenderView containing the
+  // given instance. If the instance is invalid, the ids will be 0.
+  //
+  // The PP_Instance should be already validated by the host before creating

[yzshen1, 2012/09/11 00:53:17]

I don't understand this comment. Is it out-dated or misplaced?

[brettw, 2012/09/11 20:25:20]

I clarified this a bit. I just didn't want everybody to feel like they have to
check for errors every time they call this.

+  // any resources with the PP_Instance, so you should not generally need to
+  // check for errors.
+  virtual RenderViewIDs GetRenderViewIDsForInstance(
+      PP_Instance instance) const = 0;
+
+  // Schedules the given callback to execute on the UI thread of the browser,
+  // passing the RenderView associated with the given instance as a parameter.
+  //
+  // Normally this would be called from a ResourceHost with the reply using
+  // a weak pointer to itself.
+  //
+  // Importantly, the task will not be run if the RenderView is destroyed by
+  // the time we get to the UI thread, or if the PP_Instance is invalid, but
+  // the reply will still be run. The return type in this case will be a
+  // default-constructed |ReturnType|.
+  //
+  // So you may want to make sure you don't do silly things in the reply
+  // handler if the task on the UI thread is never run and you get a
+  // default-constructed result.
+  template<typename ReturnType>
+  void PostOnUIThreadWithRenderViewAndReply(

[yzshen1, 2012/09/11 00:53:17]

This method is not used in this CL. Is it obsolete?

[brettw, 2012/09/11 20:25:20]

Yeah, I removed this and stashed it for when we need it later.

+      const tracked_objects::Location& from_here,
+      PP_Instance instance,
+      const base::Callback<ReturnType(RenderViewHost*)>& task,
+      const base::Callback<void(ReturnType)>& reply) const {
+    BrowserThread::PostTaskAndReplyWithResult(
+        BrowserThread::UI,
+        from_here,
+        base::Bind(&CallWithRenderViewHost,
+                   GetRenderViewIDsForInstance(instance), task),
+        reply);
+  }
+
  protected:
   virtual ~BrowserPpapiHost() {}
+
+  // Backend for PostOnUIThreadWithRenderViewAndReply. This converts the IDs
+  // to a RenderViewHost and calls the function, or returns a
+  // default-constructed return value on error.
+  template<typename ReturnType>
+  static ReturnType CallWithRenderViewHost(
+      const RenderViewIDs& ids,
+      const base::Callback<ReturnType(RenderViewHost*)>& task) {
+    RenderViewHost* render_view_host =
+        RenderViewHost::FromID(ids.process_id, ids.view_id);
+    if (render_view_host)
+      return task.Run(render_view_host);
+    return ReturnType();
+  }
 };
 
 }  // namespace content