This is a result of not clearing the canvas used by the HUD before drawing into it.
Created attachment 157853 [details] Patch
Comment on attachment 157853 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=157853&action=review R=me, with one robustness suggestion. > Source/WebCore/platform/graphics/chromium/cc/CCHeadsUpDisplayLayerImpl.cpp:99 > + if (canvasSize.fWidth != bounds().width() || canvasSize.fHeight != bounds().height()) If bounds() are empty the first time through this function, it'll crash on a null m_hudCanvas below. Maybe add a || !m_hudCanvas for safety?
Committed r125445: <http://trac.webkit.org/changeset/125445>