Non-composited scrollbars don't fade out when mouse is over.

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

Index: third_party/WebKit/Source/web/tests/WebFrameTest.cpp
diff --git a/third_party/WebKit/Source/web/tests/WebFrameTest.cpp b/third_party/WebKit/Source/web/tests/WebFrameTest.cpp
index 3d209f9e6ea7813e7907d879136736c0439b5854..c4077ee36b417eb519afec7fa2615eab48881717 100644
--- a/third_party/WebKit/Source/web/tests/WebFrameTest.cpp
+++ b/third_party/WebKit/Source/web/tests/WebFrameTest.cpp
@@ -10987,6 +10987,18 @@ TEST_F(WebFrameTest, TestNonCompositedOverlayScrollbarsFade) {
   testing::runDelayedTasks(kMockOverlayFadeOutDelayMs);
   EXPECT_TRUE(scrollableArea->scrollbarsHidden());
 
+  // Non-composited scrollbars don't fade out while mouse is over.
+  EXPECT_TRUE(scrollableArea->verticalScrollbar());
+  scrollableArea->setScrollOffset(ScrollOffset(20, 20), ProgrammaticScroll,
+                                  ScrollBehaviorInstant);
+  EXPECT_FALSE(scrollableArea->scrollbarsHidden());
+  scrollableArea->mouseEnteredScrollbar(*scrollableArea->verticalScrollbar());
+  testing::runDelayedTasks(kMockOverlayFadeOutDelayMs);
+  EXPECT_FALSE(scrollableArea->scrollbarsHidden());
+  scrollableArea->mouseExitedScrollbar(*scrollableArea->verticalScrollbar());
+  testing::runDelayedTasks(kMockOverlayFadeOutDelayMs);
+  EXPECT_TRUE(scrollableArea->scrollbarsHidden());
+
   mockOverlayTheme.setOverlayScrollbarFadeOutDelay(0.0);
 }