Add PluginMessageLoopProxy and use it for Host plugin UI thread.

remoting/base/plugin_message_loop_proxy.h

+// Copyright (c) 2011 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 REMOTING_BASE_PLUGIN_MESSAGE_LOOP_H_
+#define REMOTING_BASE_PLUGIN_MESSAGE_LOOP_H_
+
+#include "base/callback.h"
+#include "base/compiler_specific.h"
+#include "base/message_loop_proxy.h"
+
+namespace remoting {
+
+// MessageLoopProxy for plugin main threads.
+class PluginMessageLoopProxy : public base::MessageLoopProxy {
+ public:
+  class Delegate {
+   public:
+    Delegate() { }
+    virtual ~Delegate() { }
+
+    virtual bool RunOnPluginThread(
+        int delay_ms, void(function)(void*), void* data) = 0;

[Wez, 2011/08/15 20:28:19]

Given that there needs to be a separate Delegate implemented specific to the
plugin environment anyway, why not make this interface take a const-ref Closure,
so that it is responsible for doing any necessary heapifying, etc?  That way the
environment-specific implementation can avoid unnecessary copies and bounces
through task-runners.

[Sergey Ulanov, 2011/08/15 22:39:52]

We will need to move the closure to the heap anyway for both NPAPI and PPAPI. If
I pass void* here then it needs to be done only in one place instead of in two
delegate implementations. 
The goal is to make the delegate implementation for NPAPI and PPAPI as thin as
possible, and so the Delegate interface must be as close as possible to what is
provided by the plugin APIs.

+    virtual bool IsPluginThread() = 0;
+  };
+
+  // Caller keeps ownership of delegate.
+  PluginMessageLoopProxy(Delegate* delegate);
+  virtual ~PluginMessageLoopProxy();
+
+  void Detach();
+
+  // base::MessageLoopProxy interface.
+  virtual bool PostTask(const tracked_objects::Location& from_here,
+                        Task* task) OVERRIDE;
+  virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
+                               Task* task,
+                               int64 delay_ms) OVERRIDE;
+  virtual bool PostNonNestableTask(const tracked_objects::Location& from_here,
+                                   Task* task) OVERRIDE;

[Wez, 2011/08/15 20:28:19]

nit: Can we wrap the parameters for these three similarly to
PostNonNestableDelayedTask(), to make this block easier to read?

[Sergey Ulanov, 2011/08/15 22:39:52]

Done.

+  virtual bool PostNonNestableDelayedTask(
+      const tracked_objects::Location& from_here,
+      Task* task,
+      int64 delay_ms) OVERRIDE;
+
+  virtual bool PostTask(const tracked_objects::Location& from_here,
+                        const base::Closure& task) OVERRIDE;
+  virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
+                               const base::Closure& task,
+                               int64 delay_ms) OVERRIDE;
+  virtual bool PostNonNestableTask(const tracked_objects::Location& from_here,
+                                   const base::Closure& task) OVERRIDE;
+  virtual bool PostNonNestableDelayedTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task,
+      int64 delay_ms) OVERRIDE;
+
+  virtual bool BelongsToCurrentThread() OVERRIDE;
+
+ private:
+  // |lock_| must be acquired when accessing |delegate_|.
+  base::Lock lock_;
+  Delegate* delegate_;
+
+  static void RunTask(void* data);
+  static void RunClosure(void* data);
+
+  DISALLOW_COPY_AND_ASSIGN(PluginMessageLoopProxy);
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_BASE_PLUGIN_MESSAGE_LOOP_H_