[Sensors] Improvements in shared buffer managing

device/generic_sensor/platform_sensor_provider_base.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/platform_sensor_provider_base.h"
 
 #include <utility>
 
 #include "base/stl_util.h"
 #include "device/generic_sensor/public/interfaces/sensor_provider.mojom.h"
 
 namespace device {
 
 namespace {
 
 const uint64_t kSharedBufferSizeInBytes =
-    mojom::SensorInitParams::kReadBufferSize *
+    PlatformSensor::kReadingBufferSize *
     static_cast<uint64_t>(mojom::SensorType::LAST);
 
 }  // namespace
 
 PlatformSensorProviderBase::PlatformSensorProviderBase() = default;
 PlatformSensorProviderBase::~PlatformSensorProviderBase() = default;
 
 scoped_refptr<PlatformSensor> PlatformSensorProviderBase::CreateSensor(
-    mojom::SensorType type,
-    uint64_t size,
-    uint64_t offset) {
+    mojom::SensorType type) {
   DCHECK(CalledOnValidThread());
 
   if (!CreateSharedBufferIfNeeded())
     return nullptr;
 
-  mojo::ScopedSharedBufferMapping mapping =
-      shared_buffer_handle_->MapAtOffset(size, offset);
+  mojo::ScopedSharedBufferMapping mapping = shared_buffer_handle_->MapAtOffset(
+      PlatformSensor::kReadingBufferSize, GetSharedBufferOffset(type));
   if (!mapping)
     return nullptr;
 
   scoped_refptr<PlatformSensor> new_sensor =
-      CreateSensorInternal(type, std::move(mapping), size);
+      CreateSensorInternal(type, std::move(mapping));
   if (!new_sensor)
     return nullptr;
 
   DCHECK(!ContainsKey(sensor_map_, type));
   sensor_map_[type] = new_sensor.get();
 
   return new_sensor;
 }
 
 scoped_refptr<PlatformSensor> PlatformSensorProviderBase::GetSensor(
@@ skipping 25 matching lines @@
     shared_buffer_handle_.reset();
 }
 
 mojo::ScopedSharedBufferHandle
 PlatformSensorProviderBase::CloneSharedBufferHandle() {
   DCHECK(CalledOnValidThread());
   CreateSharedBufferIfNeeded();
   return shared_buffer_handle_->Clone();
 }
 
+uint64_t PlatformSensorProviderBase::GetSharedBufferOffset(
+    mojom::SensorType type) {
+  return (static_cast<uint64_t>(mojom::SensorType::LAST) -
+          static_cast<uint64_t>(type)) *
+         PlatformSensor::kReadingBufferSize;
+}
+
 }  // namespace device