Hard codes ScrollbarThemeGtkOrAura::scrollbarThickness to 15 in layout test mode

Source/platform/scroll/ScrollbarThemeGtkOrAura.cpp

 /*
  * Copyright (c) 2008, 2009, 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:
  *
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  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 44 matching lines @@
         return &theme;
     }
 
     DEFINE_STATIC_LOCAL(ScrollbarThemeGtkOrAura, theme, ());
     return &theme;
 }
 
 int ScrollbarThemeGtkOrAura::scrollbarThickness(ScrollbarControlSize controlSize)
 {
     // Horiz and Vert scrollbars are the same thickness.
+    // In unit tests we don't have the mock theme engine (because of layering violations), so we hard code the size (see bug 327470).
+    if (useMockTheme())
+        return 15;
     IntSize scrollbarSize = blink::Platform::current()->themeEngine()->getSize(blink::WebThemeEngine::PartScrollbarVerticalTrack);
     return scrollbarSize.width();
 }
 
 void ScrollbarThemeGtkOrAura::paintTrackPiece(GraphicsContext* gc, ScrollbarThemeClient* scrollbar, const IntRect& rect, ScrollbarPart partType)
 {
     blink::WebThemeEngine::State state = scrollbar->hoveredPart() == partType ? blink::WebThemeEngine::StateHover : blink::WebThemeEngine::StateNormal;
 
     if (useMockTheme() && !scrollbar->enabled())
         state = blink::WebThemeEngine::StateDisabled;
@@ skipping 87 matching lines @@
     if (scrollbar->orientation() == VerticalScrollbar) {
         IntSize size = blink::Platform::current()->themeEngine()->getSize(blink::WebThemeEngine::PartScrollbarVerticalThumb);
         return size.height();
     }
 
     IntSize size = blink::Platform::current()->themeEngine()->getSize(blink::WebThemeEngine::PartScrollbarHorizontalThumb);
     return size.width();
 }
 
 } // namespace WebCore