Shard webcore_svg on win official

Causing compile failures on Win x64 in Official config: http://build.chromium.org/p/chromium.perf/builders/Win%20x64%20Builder/
which this should alleviate.

R=dpranke@chromium.org
BUG=327165

Review URL: https://codereview.chromium.org/273443004

git-svn-id: svn://svn.chromium.org/blink/trunk@173433 bbb929c8-8fbe-4397-9dbb-9b2b20218538