Fix exposure of uninitialized memory in getImageData
Fix exposure of uninitialized memory in getImageData

When reading back from an accelerated canvas, we must force
the initialization of the readback destination buffer in case
the readback fails silently.

BUG=514758

Review URL: https://codereview.chromium.org/1259593008

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@199913 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk