Unreviewed, rolling out r177223 and r177226.

Unreviewed, rolling out r177223 and r177226.
https://bugs.webkit.org/show_bug.cgi?id=139631

Multiple tests are flakily asserting in
StyleResolver::loadPendingResources (Requested by ap_ on
#webkit).

Reverted changesets:

"[SVG Masking] Enable the use of <mask> elements for -webkit-
mask-image"
https://bugs.webkit.org/show_bug.cgi?id=139294
http://trac.webkit.org/changeset/177223

"animations/cross-fade-webkit-mask-image.html is flaky"
https://bugs.webkit.org/show_bug.cgi?id=139590
http://trac.webkit.org/changeset/177226

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@177266 268f45cc-cd09-0410-ab3c-d52691b4dbfc