Use correct ScrollbarTheme to paintScrollCorner

third_party/WebKit/Source/core/paint/FramePainter.cpp

Index: third_party/WebKit/Source/core/paint/FramePainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/FramePainter.cpp b/third_party/WebKit/Source/core/paint/FramePainter.cpp
index 447f20c8db45d7eb37087094a254490b83302eac..7e5fce775a81d4372cd38cd30e16f128ccc9882e 100644
--- a/third_party/WebKit/Source/core/paint/FramePainter.cpp
+++ b/third_party/WebKit/Source/core/paint/FramePainter.cpp
@@ -228,8 +228,18 @@ void FramePainter::paintScrollCorner(GraphicsContext& context,
     return;
   }
 
-  ScrollbarTheme::theme().paintScrollCorner(context, *frameView().layoutView(),
-                                            cornerRect);
+  ScrollbarTheme* theme = nullptr;
+
+  if (frameView().horizontalScrollbar()) {
+    theme = &frameView().horizontalScrollbar()->theme();
+  } else if (frameView().verticalScrollbar()) {
+    theme = &frameView().verticalScrollbar()->theme();
+  } else {
+    NOTREACHED();
+    theme = &ScrollbarTheme::theme();

[bokan, 2017/03/13 21:33:52]

style guide says don't handle failing DCHECKs:
https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md...

So if you're confident we never reach this case (I think we should only ever
paint a scroll corner if we have both scrollbars) then remove the theme = ...
line. If there are cases where we hit this then remove the NOTREACHED.

+  }
+
+  theme->paintScrollCorner(context, *frameView().layoutView(), cornerRect);
 }
 
 void FramePainter::paintScrollbar(GraphicsContext& context,