Implement PollingThread for Device Motion.

content/browser/device_orientation/data_fetcher_shared_memory_default.cc

Index: content/browser/device_orientation/data_fetcher_shared_memory_default.cc
diff --git a/content/browser/device_orientation/data_fetcher_shared_memory_default.cc b/content/browser/device_orientation/data_fetcher_shared_memory_default.cc
index 819605cb8abbfbe2728dd7e01bc4bc1f029ca102..0f66fc797730a0d4a1751f31e1f54e005b39b92e 100644
--- a/content/browser/device_orientation/data_fetcher_shared_memory_default.cc
+++ b/content/browser/device_orientation/data_fetcher_shared_memory_default.cc
@@ -9,7 +9,8 @@
 namespace content {
 
 DataFetcherSharedMemory::~DataFetcherSharedMemory() {
-  StopFetchingDeviceMotionData();
+  if (started_)
+    StopFetchingDeviceMotionData();
 }
 
 bool DataFetcherSharedMemory::NeedsPolling() {
@@ -24,9 +25,11 @@ bool DataFetcherSharedMemory::FetchDeviceMotionDataIntoBuffer() {
 bool DataFetcherSharedMemory::StartFetchingDeviceMotionData(
     DeviceMotionHardwareBuffer* buffer) {
   DCHECK(buffer);
+  device_motion_buffer_ = buffer;
   device_motion_buffer_->seqlock.WriteBegin();
   device_motion_buffer_->data.allAvailableSensorsAreActive = true;
   device_motion_buffer_->seqlock.WriteEnd();
+  started_ = true;
   return true;
 }
 
@@ -34,6 +37,7 @@ void DataFetcherSharedMemory::StopFetchingDeviceMotionData() {
   device_motion_buffer_->seqlock.WriteBegin();
   device_motion_buffer_->data.allAvailableSensorsAreActive = false;
   device_motion_buffer_->seqlock.WriteEnd();
+  started_ = false;
 }
 
 }  // namespace content