Implement the content/renderer and content/browser part of the Device Motion API.

content/browser/renderer_host/device_motion_browser_message_filter.cc

+// 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.
+
+#include "content/browser/renderer_host/device_motion_browser_message_filter.h"
+
+#include "content/browser/device_orientation/device_motion_service.h"
+#include "content/common/device_motion_messages.h"
+
+namespace content {
+
+DeviceMotionBrowserMessageFilter::DeviceMotionBrowserMessageFilter()
+    : is_started_(false) {
+}
+
+DeviceMotionBrowserMessageFilter::~DeviceMotionBrowserMessageFilter() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  if (is_started_)
+    DeviceMotionService::GetInstance()->RemoveConsumer();
+}
+
+bool DeviceMotionBrowserMessageFilter::OnMessageReceived(
+    const IPC::Message& message,
+    bool* message_was_ok) {
+  bool handled = true;
+  IPC_BEGIN_MESSAGE_MAP_EX(DeviceMotionBrowserMessageFilter,
+                           message,
+                           *message_was_ok)
+    IPC_MESSAGE_HANDLER(DeviceMotionHostMsg_StartPolling,
+                        OnDeviceMotionStartPolling)
+    IPC_MESSAGE_HANDLER(DeviceMotionHostMsg_StopPolling,
+                        OnDeviceMotionStopPolling)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP_EX()
+  return handled;
+}
+
+void DeviceMotionBrowserMessageFilter::OnDeviceMotionStartPolling() {
+  if (!is_started_) {

[darin (slow to review), 2013/06/24 23:40:34]

nit: Consider returning early when is_started_ is already true.  That way the
body of the function doesn't have to be indented.  This is just a general style
suggestion (not required).

[timvolodine, 2013/06/25 03:36:07]

Done.

+    is_started_ = true;
+    DeviceMotionService::GetInstance()->AddConsumer();
+    DidStartDeviceMotionPolling();
+  } else {
+    // Currently we only expect the renderer to tell us once to start.
+    NOTREACHED();

[darin (slow to review), 2013/06/24 23:40:34]

Note that in release builds, this NOTREACHED will be silent.  There will be no
record of spurious DeviceMotionHostMsg_{Start,Stop}Polling messages as seen in
the field.  That seems mostly OK, but it could also be reasonable to crash the
renderer when it seems to give bad messages.

[timvolodine, 2013/06/25 03:36:07]

Ack.
Added a DCHECK to catch those messages in debug.

+  }
+}
+
+void DeviceMotionBrowserMessageFilter::OnDeviceMotionStopPolling() {
+  if (is_started_) {
+    is_started_ = false;
+    DeviceMotionService::GetInstance()->RemoveConsumer();
+  } else {
+    NOTREACHED();
+  }
+}
+
+void DeviceMotionBrowserMessageFilter::DidStartDeviceMotionPolling() {
+  Send(new DeviceMotionMsg_DidStartPolling(
+      DeviceMotionService::GetInstance()->GetSharedMemoryHandleForProcess(
+          peer_handle())));
+}
+
+}  // namespace content