Currently reload/stop button is not present in content shell. If user
has to do reload operation then only option to do that is select
the url bar and click go button.Similarly stop button is not present. To stop loading of page only option is to press back button.
Added code to support stop/reload option.

BUG=

Review URL: https://codereview.chromium.org/513183002

Cr-Commit-Position: refs/heads/master@{#292778}