Introduce browser-side plumbing for sending the lock icon status to
DevTools.
Based on the plumbing doc at [1]. estark@ co-authored much of this
commit through pair programming.
This CL adds a SecurityStyleChanged() method that is fired when the lock
icon changes. This method will be implemented in
RenderFrameDevToolsAgentHost in a follow-up CL, which will pass it on to
DevTools.
[1] https://docs.google.com/document/d/1kMU5dPi2PwQ7skbgwlfQsenYdTwOi2ya2WYla2uy0OU/edit
BUG=445359, 484395
Review URL: https://codereview.chromium.org/
1162663004
Cr-Commit-Position: refs/heads/master@{#333381}