Perf experiment: what if Vectors have a default first-append size of 4?

To be rolled into the tree when quiet, and then reverted.

BUG=285442
TBR=abarth@chromium.org

Review URL: https://codereview.chromium.org/23581009

git-svn-id: http://src.chromium.org/svn/trunk/src/build@221618 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -1891,6 +1891,7 @@
       # Set this to use the new DX11 version of ANGLE.
       # TODO(apatrick): Remove this when the transition is complete.
       'ANGLE_DX11',
+      'WTF_VECTOR_INITIAL_SIZE=4',
     ],
     'conditions': [
       ['(OS=="mac" or OS=="ios") and asan==1', {