Aura overlay scrollbars shouldn't invalidate thumb on scroll or enabled state.

third_party/WebKit/Source/platform/BUILD.gn

Index: third_party/WebKit/Source/platform/BUILD.gn
diff --git a/third_party/WebKit/Source/platform/BUILD.gn b/third_party/WebKit/Source/platform/BUILD.gn
index d45fa60f61b735f57de7498d307ca52ad149ee75..4e9afef8e62b4fc4e5d33dbddd13cf986f09f381 100644
--- a/third_party/WebKit/Source/platform/BUILD.gn
+++ b/third_party/WebKit/Source/platform/BUILD.gn
@@ -1832,6 +1832,7 @@ test("blink_platform_unittests") {
 
   if (use_default_render_theme) {
     sources += [ "scroll/ScrollbarThemeAuraTest.cpp" ]
+    sources += [ "scroll/ScrollbarThemeOverlayTest.cpp" ]

[jbroman, 2016/12/22 15:21:00]

If you leave this here, put these in one list:

sources += [
  "scroll/ScrollbarThemeAuraTest.cpp",
  "scroll/ScrollbarThemeOverlayTest.cpp",
]

But ScrollbarThemeOverlay seems to be built in !use_default_render_theme builds
too, so why is this not just in the main unit test file list?

[bokan, 2016/12/22 16:10:55]

Good catch, I just put it beside the AuraTest without thinking too much. Moved
to main unittest list above.

   }
 
   sources += [ "testing/RunAllTests.cpp" ]