cc: Remove the --enable-partial-swap flag.

This flag only affects the cc::GLRenderer which is only
used when ubercomp is disabled. This means non-aura platforms.

On these platforms, the --enable-partial-swap flag is
never set, so we can turn it off permanently for non-ubercomp
renderer compositors. This removes the whole "AllowPartialSwap"
concept from content/renderer/ along with the command line
flag.


R=piman
BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=251898

Review URL: https://codereview.chromium.org/167953003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252362 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252362