[sensors] PlatformSensorProvider implementations are notified when there are no sensor instances

device/generic_sensor/BUILD.gn

 # 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.
 
 import("//build/config/features.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")  # For generate_jni().
 }
 
@@ skipping 68 matching lines @@
     "fake_platform_sensor.cc",
     "fake_platform_sensor.h",
     "fake_platform_sensor_provider.cc",
     "fake_platform_sensor_provider.h",
   ]
 
   public_deps = [
     ":generic_sensor",
     "//base",
     "//device/generic_sensor/public/interfaces",
+    "//testing/gmock",
   ]
 }