Fix race condition in DataFetcherSharedMemoryBase

content/browser/device_orientation/data_fetcher_shared_memory_mac.cc

 // Copyright 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 "data_fetcher_shared_memory.h"
 
 #include "base/logging.h"
 #include "third_party/sudden_motion_sensor/sudden_motion_sensor_mac.h"
 
 namespace {
@@ skipping 97 matching lines @@
   if (consumer_bitmask & CONSUMER_TYPE_ORIENTATION)
     FetchOrientation(sudden_motion_sensor_.get(), orientation_buffer_);
   if (consumer_bitmask & CONSUMER_TYPE_MOTION)
     FetchMotion(sudden_motion_sensor_.get(), motion_buffer_);
 }
 
 bool DataFetcherSharedMemory::IsPolling() const {
   return true;
 }
 
-bool DataFetcherSharedMemory::Start(ConsumerType consumer_type) {
+bool DataFetcherSharedMemory::Start(ConsumerType consumer_type, void* buffer) {
   DCHECK(base::MessageLoop::current() == GetPollingMessageLoop());
-
-  void* buffer = GetSharedMemoryBuffer(consumer_type);
   DCHECK(buffer);
 
   switch (consumer_type) {
     case CONSUMER_TYPE_MOTION:
       motion_buffer_ = static_cast<DeviceMotionHardwareBuffer*>(buffer);
       if (!sudden_motion_sensor_)
         sudden_motion_sensor_.reset(SuddenMotionSensor::Create());
       return true;
     case CONSUMER_TYPE_ORIENTATION:
       orientation_buffer_ =
@@ skipping 27 matching lines @@
         orientation_buffer_ = NULL;
       }
       return true;
     default:
       NOTREACHED();
   }
   return false;
 }
 
 }  // namespace content