[Reland] [DevTools] Respect kDisallowedForForceInstalledExtensions policy value

This is a reland of CL:1069411 (which has been reverted in CL:1094734)
Original Author is dgozman@chromium.org.

Added a helper to ChromeDevToolsManagerDelegate and DevToolsWindow
to check whether inspection is allowed. This helper is used to:
- not open DevToolsWindow;
- not show "Inspect Element" context menu item;
- disable DevTools-related browser commands;
- not show inspectable views on chrome://extensions;
- not show extensions on chrome://inspect.

RenderFrameDevToolsAgentHost also disallows attaching a debugging session
when embedder says so to prevent exposure over protocol or remote debugging.

TBR=avi@chromium.org,rdevlin.cronin@chromium.org
(TBR-ed due to no changes in OWNER-ed files this reland CL since the original
 CL:1069411)

Bug: 838146
Test: browser_tests --gtest_filter=DevToolsSanity*Policy*
Change-Id: I2c26bce4f0be57e8b526b7fff73442712d46d5da
Reviewed-on: https://chromium-review.googlesource.com/1125855


Commit-Queue: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572616}