Suppressing the valgrind error probably caused by WebKit r47756....

tools/valgrind/memcheck/suppressions.txt

 # There are three kinds of suppressions in this file.
 # 1. third party stuff we have no control over
 #
 # 2. intentional unit test errors, or stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing
 #
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 # These should all be in chromium's bug tracking system (but a few aren't yet).
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 1128 matching lines @@
    bug_20941
    Memcheck:Cond
    fun:_ZNK7WebCore23RenderThemeChromiumSkia21adjustSliderThumbSizeEPNS_12RenderObjectE
    fun:_ZN7WebCore12RenderSlider6layoutEv
    ...
    fun:_ZN7WebCore10RenderView6layoutEv
    fun:_ZN7WebCore9FrameView6layoutEb
    fun:_ZN7WebCore8Document12updateLayoutEv
 }
 {
+   bug_20941
+   Memcheck:Value4
+   fun:_ZNK7WebCore23RenderThemeChromiumSkia21adjustSliderThumbSizeEPNS_12RenderObjectE
+}
+{
    bug_20964
    Memcheck:Cond
    ...
    fun:_ZN7WebCore7makeRGBEiii
 }
 {
    bug_20964
    Memcheck:Value4
    ...
    fun:_ZN7WebCore7makeRGBEiii
 }