Inject timestamps to resource messages.

content/common/child_resource_message_filter.h

Index: content/common/child_resource_message_filter.h
diff --git a/content/common/child_resource_message_filter.h b/content/common/child_resource_message_filter.h
new file mode 100644
index 0000000000000000000000000000000000000000..436d948b67d45c28ef2ea436abd8b82d830e2a2d
--- /dev/null
+++ b/content/common/child_resource_message_filter.h
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+// Copyright (c) 2013 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 CONTENT_COMMON_CHILD_RESOURCE_MESSAGE_FILTER_H_
+#define CONTENT_COMMON_CHILD_RESOURCE_MESSAGE_FILTER_H_
+
+#include "base/memory/ref_counted.h"
+#include "ipc/ipc_channel_proxy.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace content {
+class ResourceDispatcher;
+
+// Supplies ResourceDispatcher with timestamps for some resource messages.
+//
+// Background: ResourceDispatcher converts browser process time to child
+// process time. This is done to achieve coherent timeline. Conversion is
+// a linear transformation such that given browser process time range is
+// mapped to corresponding child process time range. Timestamps for child
+// process time range should be taken by IO thread when resource messages
+// arrive. Otherwise, timestamps may be affected by long rendering / JS task.
+//
+// When specific message is processed by this filter, new task charged
+// with timestamp is posted to main thread. This task is processed just before
+// resource message and invokes ResourceDispatcher::set_io_timestamp.
+class ChildResourceMessageFilter : public IPC::ChannelProxy::MessageFilter {
+ public:
+  explicit ChildResourceMessageFilter(ResourceDispatcher* resource_dispatcher);
+
+  // IPC::ChannelProxy::MessageFilter implementation.
+  virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
+
+ private:
+  virtual ~ChildResourceMessageFilter();
+
+  scoped_refptr<base::SingleThreadTaskRunner> main_thread_task_runner_;
+  ResourceDispatcher* resource_dispatcher_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChildResourceMessageFilter);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_CHILD_RESOURCE_MESSAGE_FILTER_H_