Fix scrollbar buttons at hidpi when enable-use-zoom-for-dsf is on.

third_party/WebKit/Source/platform/blink_platform.gypi

Index: third_party/WebKit/Source/platform/blink_platform.gypi
diff --git a/third_party/WebKit/Source/platform/blink_platform.gypi b/third_party/WebKit/Source/platform/blink_platform.gypi
index 26243272a446fb8f98f452d66aa66d10f7e2f723..6631dc1348be81c74a9cd67de28b3d7232a387d1 100644
--- a/third_party/WebKit/Source/platform/blink_platform.gypi
+++ b/third_party/WebKit/Source/platform/blink_platform.gypi
@@ -1322,6 +1322,13 @@
           ],
         }
       ],
+      ['use_default_render_theme==1',
+        {
+          'platform_test_files': [
+            'scroll/ScrollbarThemeAuraTest.cpp',
+          ],
+        }
+      ],
     ],
   },
 }