Use a valid ChromeOS #define in MouseWheelEventQueueTest

MouseWheelEventQueueTest uses a non-existent #define for ChromeOS,
defined(CHROME_OS), we should replace it with defined(OS_CHROMEOS).

Bug: 1121653
Change-Id: Ia6ee5adf638aad3d25d03f36d0903c509d793ecd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2433304Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811346}

content/browser/renderer_host/input/mouse_wheel_event_queue_unittest.cc

@@ -127,7 +127,7 @@ const float kWheelScrollGlobalY = 72;
   EXPECT_EQ(WebGestureEvent::InertialPhaseState::kMomentum, \
             event->data.scroll_end.inertial_phase);
 
-#if defined(CHROME_OS)
+#if defined(OS_CHROMEOS)
 #define EXPECT_SYNTHETIC_INERTIAL_GESTURE_SCROLL_END(event) \
   EXPECT_GESTURE_SCROLL_END_IMPL(event);                    \
   EXPECT_TRUE(event->data.scroll_end.synthetic);            \
@@ -459,7 +459,7 @@ TEST_F(MouseWheelEventQueueTest,
 // Tests that a Wheel event with synthetic momentumn_phase == PhaseEnded that is
 // generated by the fling controller properly populates
 // scroll_end.data.scroll_end.generated_by_fling_controller.
-#if defined(CHROME_OS)
+#if defined(OS_CHROMEOS)
 TEST_F(MouseWheelEventQueueTest, WheelEndWithMomentumPhaseEndedInformation) {
   const ui::ScrollGranularity scroll_units =
       ui::ScrollGranularity::kScrollByPrecisePixel;
@@ -488,7 +488,7 @@ TEST_F(MouseWheelEventQueueTest, WheelEndWithMomentumPhaseEndedInformation) {
   EXPECT_SYNTHETIC_INERTIAL_GESTURE_SCROLL_END(sent_gesture_event(0));
   EXPECT_EQ(1U, GetAndResetSentEventCount());
 }
-#endif  // defined(CHROME_OS)
+#endif  // defined(OS_CHROMEOS)
 
 TEST_F(MouseWheelEventQueueTest, GestureSendingInterrupted) {
   const ui::ScrollGranularity scroll_units =