Replace CHROMEOS macro with OS_CHROMEOS

CHROMEOS macro is defined in third_party/webrtc.
This CL replaces it with more appropriate macro.

Bug: None
Change-Id: Ib027e5f8c35f5318919f515d97a22d3991607ca8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2022126
Commit-Queue: David Bokan <bokan@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735395}

content/browser/renderer_host/input/fling_browsertest.cc

@@ -390,7 +390,7 @@ IN_PROC_BROWSER_TEST_F(BrowserSideFlingBrowserTest,
 }
 
 // Touchpad fling only happens on ChromeOS.
-#if defined(CHROMEOS)
+#if defined(OS_CHROMEOS)
 IN_PROC_BROWSER_TEST_F(BrowserSideFlingBrowserTest,
                        TouchpadInertialGSUsBubbleFromOOPIF) {
   LoadPageWithOOPIF();
@@ -408,7 +408,7 @@ IN_PROC_BROWSER_TEST_F(BrowserSideFlingBrowserTest,
   SimulateTouchpadFling(child_view_->host(), GetWidgetHost(), fling_velocity);
   WaitForFrameScroll(GetRootNode(), 15, true /* upward */);
 }
-#endif  // defined(CHROMEOS)
+#endif  // defined(OS_CHROMEOS)
 
 IN_PROC_BROWSER_TEST_F(BrowserSideFlingBrowserTest,
                        InertialGSEGetsBubbledFromOOPIF) {