Revert 173540 "Use skia discardable memory for decoded images on..."

Appears to break webkit_unit_tests:
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Android%20%28Nexus4%29/builds/13112

> Use skia discardable memory for decoded images on Android.
> 
> BUG=330041
> 
> Review URL: https://codereview.chromium.org/266633010

TBR=reveman@chromium.org

Review URL: https://codereview.chromium.org/274563005

git-svn-id: svn://svn.chromium.org/blink/trunk@173569 bbb929c8-8fbe-4397-9dbb-9b2b20218538