[Sensors] Improvements in shared buffer managing

device/generic_sensor/sensor_provider_impl.cc

 // Copyright 2016 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 "device/generic_sensor/sensor_provider_impl.h"
 
 #include <utility>
 
 #include "device/generic_sensor/platform_sensor_provider.h"
 #include "device/generic_sensor/sensor_impl.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 
 namespace device {
 
-namespace {
-
-uint64_t GetBufferOffset(mojom::SensorType type) {
-  return (static_cast<uint64_t>(mojom::SensorType::LAST) -
-          static_cast<uint64_t>(type)) *
-         mojom::SensorInitParams::kReadBufferSize;
-}
-
-}  // namespace
-
 // static
 void SensorProviderImpl::Create(mojom::SensorProviderRequest request) {
   PlatformSensorProvider* provider = PlatformSensorProvider::GetInstance();
   if (provider) {
     mojo::MakeStrongBinding(base::WrapUnique(new SensorProviderImpl(provider)),
                             std::move(request));
   }
 }
 
 SensorProviderImpl::SensorProviderImpl(PlatformSensorProvider* provider)
     : provider_(provider) {
   DCHECK(provider_);
 }
 
 SensorProviderImpl::~SensorProviderImpl() {}
 
 void SensorProviderImpl::GetSensor(mojom::SensorType type,
                                    mojom::SensorRequest sensor_request,
                                    const GetSensorCallback& callback) {
   auto cloned_handle = provider_->CloneSharedBufferHandle();
   if (!cloned_handle.is_valid()) {
     callback.Run(nullptr, nullptr);
     return;
   }
 
   scoped_refptr<PlatformSensor> sensor = provider_->GetSensor(type);
   if (!sensor) {
-    sensor = provider_->CreateSensor(
-        type, mojom::SensorInitParams::kReadBufferSize, GetBufferOffset(type));
+    sensor = provider_->CreateSensor(type);
   }
 
   if (!sensor) {
     callback.Run(nullptr, nullptr);
     return;
   }
 
   auto sensor_impl = base::MakeUnique<SensorImpl>(sensor);
 
   auto init_params = mojom::SensorInitParams::New();
   init_params->memory = std::move(cloned_handle);
-  init_params->buffer_offset = GetBufferOffset(type);
+  init_params->buffer_offset = provider_->GetSharedBufferOffset(type);
   init_params->mode = sensor->GetReportingMode();
   init_params->default_configuration = sensor->GetDefaultConfiguration();
 
   callback.Run(std::move(init_params), sensor_impl->GetClient());
 
   mojo::MakeStrongBinding(std::move(sensor_impl), std::move(sensor_request));
 }
 
 }  // namespace device