Remove plumbing for the inert-visual-viewport flag.

Note that the Blink setting inertVisualViewport still exists and is set to false by default.
A follow up CL will set this to true once dependent tests are fixed.

BUG=489206

Review URL: https://codereview.chromium.org/1415513002

Cr-Commit-Position: refs/heads/master@{#355907}
16 files changed