Remove template instantiation in the header file.

We got some errors in link stage when using distributed thinlto
renderer_blink_platform_impl.o.thinlto.o:renderer_blink_platform_impl.cc:vtable
for content::DeviceSensorEventPump<blink::WebDeviceMotionListener>: warning:
relocation refers to discarded section
Removing the template instantiation statement fixes this issue.

BUG=820514
TEST=emerge-samus chromeos-chrome

Change-Id: I24a8221d576adac0495ff44c7d8d110aecc586fd
Reviewed-on: https://chromium-review.googlesource.com/946681Reviewed-by: Tim Volodine <timvolodine@chromium.org>
Commit-Queue: Yunlian Jiang <yunlian@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543224}

content/renderer/device_sensors/device_motion_event_pump.cc

@@ -17,6 +17,8 @@
 
 namespace content {
 
+template class DeviceSensorEventPump<blink::WebDeviceMotionListener>;
+
 DeviceMotionEventPump::DeviceMotionEventPump(RenderThread* thread)
     : DeviceSensorEventPump<blink::WebDeviceMotionListener>(thread),
       accelerometer_(this, device::mojom::SensorType::ACCELEROMETER),

content/renderer/device_sensors/device_orientation_event_pump.cc

@@ -41,6 +41,8 @@ bool IsSignificantlyDifferent(const device::OrientationData& data1,
 
 namespace content {
 
+template class DeviceSensorEventPump<blink::WebDeviceOrientationListener>;
+
 const double DeviceOrientationEventPump::kOrientationThreshold = 0.1;
 
 DeviceOrientationEventPump::DeviceOrientationEventPump(RenderThread* thread,

content/renderer/device_sensors/device_sensor_event_pump.h

@@ -324,10 +324,6 @@ class CONTENT_EXPORT DeviceSensorEventPump
 
   DISALLOW_COPY_AND_ASSIGN(DeviceSensorEventPump);
 };
-
-template class DeviceSensorEventPump<blink::WebDeviceMotionListener>;
-template class DeviceSensorEventPump<blink::WebDeviceOrientationListener>;
-
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_DEVICE_SENSORS_DEVICE_SENSOR_EVENT_PUMP_H_