blink: Remove uses of blink variant bindings in content

Including a blink variant binding in content/renderer means that
content/renderer includes all of wtf/. Sadly this means that we can
no longer use the same enum in content/renderer and blink so we
static cast at the boundary.

Review-Url: https://codereview.chromium.org/2145993003
Cr-Commit-Position: refs/heads/master@{#405498}
4 files changed