Implement PollingThread for Device Motion.

content/browser/device_orientation/data_fetcher_shared_memory_android.cc

Index: content/browser/device_orientation/data_fetcher_shared_memory_android.cc
diff --git a/content/browser/device_orientation/data_fetcher_shared_memory_android.cc b/content/browser/device_orientation/data_fetcher_shared_memory_android.cc
index 5a87c6d32e4b859130482bbb610901492bec7765..c35cda63ef752a14b214410cbdf5dd78db4fe167 100644
--- a/content/browser/device_orientation/data_fetcher_shared_memory_android.cc
+++ b/content/browser/device_orientation/data_fetcher_shared_memory_android.cc
@@ -10,7 +10,8 @@
 namespace content {
 
 DataFetcherSharedMemory::~DataFetcherSharedMemory() {
-  StopFetchingDeviceMotionData();
+  if (started_)
+    StopFetchingDeviceMotionData();
 }
 
 bool DataFetcherSharedMemory::NeedsPolling() {
@@ -24,13 +25,16 @@ bool DataFetcherSharedMemory::FetchDeviceMotionDataIntoBuffer() {
 
 bool DataFetcherSharedMemory::StartFetchingDeviceMotionData(
     DeviceMotionHardwareBuffer* buffer) {
+  DCHECK(buffer);
   device_motion_buffer_ = buffer;
   return DataFetcherImplAndroid::GetInstance()->
       StartFetchingDeviceMotionData(buffer);
+  started_ = true;
 }
 
 void DataFetcherSharedMemory::StopFetchingDeviceMotionData() {
     DataFetcherImplAndroid::GetInstance()->StopFetchingDeviceMotionData();
+    started_ = false;
 }
 
 }  // namespace content