Roll src/third_party/WebKit abc2d6b:7af3c4a (svn 190692:190696)

Summary of changes available at:
https://chromium.googlesource.com/chromium/blink/+log/abc2d6b..7af3c4a

TBR=zmo@chromium.org,hiroshige@chromium.org

Review URL: https://codereview.chromium.org/938823006

Cr-Commit-Position: refs/heads/master@{#317729}

DEPS

@@ -34,7 +34,7 @@ vars = {
   'llvm_url': 'http://src.chromium.org/llvm-project',
   'llvm_git': 'https://llvm.googlesource.com',
   'webkit_trunk': 'http://src.chromium.org/blink/trunk',
-  'webkit_revision': 'abc2d6bf20f762f347184693af19d9c391acb3ed', # from svn revision 190692
+  'webkit_revision': '7af3c4ab755f66f12b32484b7811e7d07ed5191c', # from svn revision 190696
   'chromium_git': 'https://chromium.googlesource.com',
   'chromiumos_git': 'https://chromium.googlesource.com/chromiumos',
   'pdfium_git': 'https://pdfium.googlesource.com',