Revert "GYP variable v8_optimized_debug should be overridable by GYP_DEFINES"

This reverts r226772; it looks like this broke the default behavior
when the variable was not set in GYP_DEFINES.

TBR=jkummerow@chromium.org, rafaelw@chromium.org
BUG=

Review URL: https://codereview.chromium.org/25932002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226843 0039d316-1c4b-4281-b951-d872f2087c98
[Android WebView] Change default tile size to 512x512

This is to reduce the number of gpu memory buffer allocations which
can consume multiple file descriptors.

BUG=
NOTRY=true

Review URL: https://codereview.chromium.org/25930002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226844 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226844