Roll src/third_party/WebKit 9122ec7:642a2fa (svn 201579:201580)

Summary of changes available at:
https://chromium.googlesource.com/chromium/blink/+log/9122ec7..642a2fa

Sheriffs: In case of breakage, do NOT revert this roll, revert the
offending commit in the blink repository instead.

NOTRY=true
TBR=schenney@chromium.org,mlamouri@chromium.org,falken@chromium.org

Review URL: https://codereview.chromium.org/1327723003

Cr-Commit-Position: refs/heads/master@{#346773}

DEPS

@@ -31,7 +31,7 @@ vars = {
   # Use this googlecode_url variable only if there is an internal mirror for it.
   # If you do not know, use the full path while defining your new deps entry.
   'googlecode_url': 'http://%s.googlecode.com/svn',
-  'webkit_revision': '9122ec7bdfc0e5d43fe48185694ad19c86fb9217', # from svn revision 201579
+  'webkit_revision': '642a2fa76d466ca307b2bcfac8de24a0b23325a6', # from svn revision 201580
   'chromium_git': 'https://chromium.googlesource.com',
   'libvpx_revision': 'a208ecae8e6fff1c0d4286bdc000d7c5efaab411',
   'sfntly_revision': '1bdaae8fc788a5ac8936d68bf24f37d977a13dac',