[DeviceLight] Ensure to round lux value to avoid fingerprinting risk.

third_party/WebKit/Source/modules/device_light/DeviceLightDispatcher.cpp

 // Copyright 2014 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 "modules/device_light/DeviceLightDispatcher.h"
 
+#include <cmath>
+
 #include "modules/device_light/DeviceLightController.h"
 #include "public/platform/Platform.h"
 
+namespace {
+double EnsureRoundedLuxValue(double lux) {
+  // Make sure to round the lux value to nearest integer, to
+  // avoid too precise values and hence reduce fingerprinting risk.
+  // The special case when the lux value is infinity (no data can be
+  // provided) is simply returned as is.
+  // TODO(timvolodine): consider reducing the lux value precision further.
+  return std::isinf(lux) ? lux : std::round(lux);
+}
+}  // namespace
+
 namespace blink {
 
 DeviceLightDispatcher& DeviceLightDispatcher::Instance() {
   DEFINE_STATIC_LOCAL(DeviceLightDispatcher, device_light_dispatcher,
                       (new DeviceLightDispatcher));
   return device_light_dispatcher;
 }
 
 DeviceLightDispatcher::DeviceLightDispatcher() : last_device_light_data_(-1) {}
 
 DeviceLightDispatcher::~DeviceLightDispatcher() {}
 
 DEFINE_TRACE(DeviceLightDispatcher) {
   PlatformEventDispatcher::Trace(visitor);
 }
 
 void DeviceLightDispatcher::StartListening() {
   Platform::Current()->StartListening(kWebPlatformEventTypeDeviceLight, this);
 }
 
 void DeviceLightDispatcher::StopListening() {
   Platform::Current()->StopListening(kWebPlatformEventTypeDeviceLight);
   last_device_light_data_ = -1;
 }
 
 void DeviceLightDispatcher::DidChangeDeviceLight(double value) {
-  last_device_light_data_ = value;
-  NotifyControllers();
+  double newValue = EnsureRoundedLuxValue(value);
+  if (last_device_light_data_ != newValue) {
+    last_device_light_data_ = newValue;
+    NotifyControllers();
+  }
 }
 
 double DeviceLightDispatcher::LatestDeviceLightData() const {
   return last_device_light_data_;
 }
 
 }  // namespace blink