Roll src/third_party/WebKit 234f749:477efb1 (svn 189290:189299)

Summary of changes available at:
https://chromium.googlesource.com/chromium/blink/+log/234f749..477efb1

TBR=

Review URL: https://codereview.chromium.org/886443005

Cr-Commit-Position: refs/heads/master@{#314067}

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': '234f74988a0afc0f6074a78ae9513d7276d32fb6', # from svn revision 189290
+  'webkit_revision': '477efb10a6feb91d0786768e321e7fa960c85980', # from svn revision 189299
   'chromium_git': 'https://chromium.googlesource.com',
   'chromiumos_git': 'https://chromium.googlesource.com/chromiumos',
   'pdfium_git': 'https://pdfium.googlesource.com',