Reland "Throttle resource message requests during user interaction"

content/renderer/scheduler/throttled_message_sender.h

Index: content/renderer/scheduler/throttled_message_sender.h
diff --git a/content/renderer/scheduler/throttled_message_sender.h b/content/renderer/scheduler/throttled_message_sender.h
new file mode 100644
index 0000000000000000000000000000000000000000..14ed5b982b065a92f25adbcd02c593599978a72e
--- /dev/null
+++ b/content/renderer/scheduler/throttled_message_sender.h
@@ -0,0 +1,74 @@
+// Copyright 2015 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_RENDERER_SCHEDULER_THROTTLED_MESSAGE_SENDER_H_
+#define CONTENT_RENDERER_SCHEDULER_THROTTLED_MESSAGE_SENDER_H_
+
+#include <deque>
+
+#include "base/threading/thread_checker.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+#include "content/common/content_export.h"
+#include "ipc/ipc_sender.h"
+
+namespace content {
+
+class RendererScheduler;
+
+// Utility class for throttling a stream of IPC messages targetted to a specific
+// IPC sender. The throttling itself is very basic:
+//  * When there is no high-priority work on the main thread, as indicated by
+//    the RendererScheduler, throttling is disabled.
+//  * When >= N messages have been sent in a given time window, messages are
+//    queued. A timer periodically flushes a portion of the queued messages
+//    until all messages have been flushed.
+//  * If a sync IPC is received, all queued messages are flushed immediately.
+//
+// This simplistic approach is particularly useful for IPC types that can
+//   1) be sent at a very high rate (multiple messages per frame) and
+//   2) interrupt page responsiveness due to the induced work, particularly on
+//      the receiver's IO thread.
+// Such is the case, for example, for ResourceHostMsg_RequestResource messages.
+class CONTENT_EXPORT ThrottledMessageSender : public IPC::Sender {
+ public:
+  // |max_sent_messages_per_second| must be strictly positive.
+  ThrottledMessageSender(IPC::Sender* proxied_sender,
+                         RendererScheduler* scheduler,
+                         int max_sent_messages_per_second);
+  ~ThrottledMessageSender() override;
+
+  // IPC::Sender implementation:
+  bool Send(IPC::Message* msg) override;
+
+ protected:
+  // Virtual for testing.
+  virtual base::TimeTicks Now() const;
+
+ private:
+  friend class ThrottledMessageSenderTest;
+
+  void FlushAll();
+  void FlushThrottled();
+  bool SendViaProxiedSender(IPC::Message* msg);
+
+  base::ThreadChecker thread_checker_;
+  IPC::Sender* const proxied_sender_;
+  RendererScheduler* const scheduler_;
+
+  const int max_sent_messages_per_flush_;
+  const base::TimeDelta flush_period_;
+  base::TimeTicks last_sent_message_time_;
+  int sent_messages_since_last_flush_;
+  base::Timer flush_timer_;
+
+  std::deque<IPC::Message*> throttled_messages_;
+  bool is_sending_via_proxied_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThrottledMessageSender);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_SCHEDULER_THROTTLED_MESSAGE_SENDER_H_