Setup for moving getUserMedia to secure origins only

This makes two notable changes:
  * Removes the browser tests that verify that the getUserMedia
    permission is not "sticky" on insecure origins.
  * Moves the addition of the chrome-extension: and
    chrome-extension-resource: schemes to extensions::Dispatcher.

The former is necessary because once getUserMedia is removed from
insecure origins, the browser test will (correctly) fail. Thus this is
part of a two sided patch.

The later is necessary because extension browser tests that use
getUserMedia will start failing once the change is made, because the
tests use ShellContentRendererClient, which doesn't currently treat
chrome-extension: schemes as secure, so getUserMedia will be disallowed
by the renderer. By marking the scheme as secure in
extensions::Dispatcher instead of in
ChromeContentRendererClient::RenderThreadStarted, the schemes will be
marked as secure in ShellContentRendererClient as well, so getUserMedia
will be allowed in the browser tests.


Review URL:

Cr-Commit-Position: refs/heads/master@{#344635}
4 files changed