[sensors] Introduce asynchronous way to create sensors.

device/generic_sensor/sensor_provider_impl.cc

Index: device/generic_sensor/sensor_provider_impl.cc
diff --git a/device/generic_sensor/sensor_provider_impl.cc b/device/generic_sensor/sensor_provider_impl.cc
index 2cdb1c5a32d5b32ac3c3b97070d0a3a2f0983d33..930083a20ce4c479eab59e88f77f44bb71b690a6 100644
--- a/device/generic_sensor/sensor_provider_impl.cc
+++ b/device/generic_sensor/sensor_provider_impl.cc
@@ -20,6 +20,9 @@ uint64_t GetBufferOffset(mojom::SensorType type) {
          mojom::SensorInitParams::kReadBufferSize;
 }
 
+using CreateSensorCallback =
+    base::Callback<void(scoped_refptr<PlatformSensor>)>;
+
 }  // namespace
 
 // static
@@ -32,7 +35,7 @@ void SensorProviderImpl::Create(mojom::SensorProviderRequest request) {
 }
 
 SensorProviderImpl::SensorProviderImpl(PlatformSensorProvider* provider)
-    : provider_(provider) {
+    : provider_(provider), weak_ptr_factory_(this) {
   DCHECK(provider_);
 }
 
@@ -49,10 +52,25 @@ void SensorProviderImpl::GetSensor(mojom::SensorType type,
 
   scoped_refptr<PlatformSensor> sensor = provider_->GetSensor(type);
   if (!sensor) {
-    sensor = provider_->CreateSensor(
-        type, mojom::SensorInitParams::kReadBufferSize, GetBufferOffset(type));
+    CreateSensorCallback cb = base::Bind(
+        &SensorProviderImpl::SensorCreated, weak_ptr_factory_.GetWeakPtr(),
+        type, base::Passed(&cloned_handle), base::Passed(&sensor_request),
+        callback);
+    provider_->CreateSensor(type, mojom::SensorInitParams::kReadBufferSize,
+                            GetBufferOffset(type), cb);
+    return;
   }
 
+  SensorCreated(type, std::move(cloned_handle), std::move(sensor_request),
+                callback, std::move(sensor));
+}
+
+void SensorProviderImpl::SensorCreated(
+    mojom::SensorType type,
+    mojo::ScopedSharedBufferHandle cloned_handle,
+    mojom::SensorRequest sensor_request,
+    const GetSensorCallback& callback,
+    scoped_refptr<PlatformSensor> sensor) {
   if (!sensor) {
     callback.Run(nullptr, nullptr);
     return;