Clean-up refactoring of chrome_content_browser_client to use GetPermissionContext consistently.
Eliminate some duplicate code now that PermissionContextBase is the base class
for all other permission contexts and we have a helper function
GetPermissionContext to obtain the proper permission context class depending
on permission type. Also move PermissionToContentSetting to anonymous namespace.
BUG=
Review URL: https://codereview.chromium.org/
896173002
Cr-Commit-Position: refs/heads/master@{#314866}