Drawing bounds should not be pixel-snapped.

Source/core/paint/LayoutObjectDrawingRecorder.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef LayoutObjectDrawingRecorder_h
 #define LayoutObjectDrawingRecorder_h
 
 #include "core/layout/LayoutObject.h"
 #include "core/paint/PaintPhase.h"
 #include "platform/geometry/LayoutRect.h"
@@ skipping 25 matching lines @@
         // We may paint a delayed-invalidation object before it's actually invalidated.
         if (layoutObject.fullPaintInvalidationReason() == PaintInvalidationDelayedFull)
             m_cacheSkipper.emplace(context);
         m_drawingRecorder.emplace(context, layoutObject, displayItemType, clip);
     }
 
     LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase, const FloatRect& clip)
         : LayoutObjectDrawingRecorder(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase), clip) { }
 
     LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, DisplayItem::Type type, const LayoutRect& clip)
-        : LayoutObjectDrawingRecorder(context, layoutObject, type, pixelSnappedIntRect(clip)) { }
+        : LayoutObjectDrawingRecorder(context, layoutObject, type, enclosingIntRect(clip)) { }

[jbroman, 2015/08/24 15:58:46]

Aside: This could arguably just be "clip", which does a conversion to FloatRect.
It's not clear to me why going to the integer pixel grid here is helpful.

So far I've just used enclosingIntRect because it seems like the smaller change.

 
 #if ENABLE(ASSERT)
     void setUnderInvalidationCheckingMode(DrawingDisplayItem::UnderInvalidationCheckingMode mode) { m_drawingRecorder->setUnderInvalidationCheckingMode(mode); }
 #endif
 
 private:
     Optional<DisplayItemCacheSkipper> m_cacheSkipper;
     Optional<DrawingRecorder> m_drawingRecorder;
 };
 
 } // namespace blink
 
 #endif // LayoutObjectDrawingRecorder_h