Make SyzyAsan depend on 'syzyasan' GYP flag instead of 'asan==1 and OS=="win"'

We're bringing the regular Clang-based ASan to Windows and will put it behind
asan==1 like on all other platforms.

BUG=343960

Review URL: https://codereview.chromium.org/167773002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251518 0039d316-1c4b-4281-b951-d872f2087c98
Remove unused WebLayerTreeViewImplForTesting::composite

BUG=none

Review URL: https://codereview.chromium.org/166073008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251519 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251519