Call ScrollableArea::ShowOverlayScrollbars for explicit scrolls only.

third_party/WebKit/Source/web/tests/WebFrameTest.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 11561 matching lines @@
   scrollable_area->SetScrollOffset(ScrollOffset(10, 10), kProgrammaticScroll,
                                    kScrollBehaviorInstant);
 
   EXPECT_FALSE(scrollable_area->ScrollbarsHidden());
   testing::RunDelayedTasks(kMockOverlayFadeOutDelayMs);
   EXPECT_TRUE(scrollable_area->ScrollbarsHidden());
 
   frame->ExecuteScript(WebScriptSource(
       "document.getElementById('space').style.height = '500px';"));
   frame->View()->UpdateAllLifecyclePhases();
-
-  EXPECT_FALSE(scrollable_area->ScrollbarsHidden());
-  testing::RunDelayedTasks(kMockOverlayFadeOutDelayMs);
   EXPECT_TRUE(scrollable_area->ScrollbarsHidden());
 
   frame->ExecuteScript(WebScriptSource(
       "document.getElementById('container').style.height = '300px';"));
   frame->View()->UpdateAllLifecyclePhases();
 
   EXPECT_FALSE(scrollable_area->ScrollbarsHidden());
   testing::RunDelayedTasks(kMockOverlayFadeOutDelayMs);
   EXPECT_TRUE(scrollable_area->ScrollbarsHidden());
 
@@ skipping 402 matching lines @@
 
   // Failing the original child frame navigation and trying to render fallback
   // content shouldn't crash. It should return NoLoadInProgress. This is so the
   // caller won't attempt to replace the correctly empty frame with an error
   // page.
   EXPECT_EQ(WebLocalFrame::NoLoadInProgress,
             child->MaybeRenderFallbackContent(WebURLError()));
 }
 
 }  // namespace blink