[DevTools] Do not allow chrome.debugger to attach to web ui pages

If the page navigates to web ui, we force detach the debugger extension.

TBR=alexclarke@chromium.org

Bug: 798222
Change-Id: Idb46c2f59e839388397a8dfa6ce2e2a897698df3
Reviewed-on: https://chromium-review.googlesource.com/935961
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540916}
void RenderFrameDevToolsAgentHost::DestroyOnRenderFrameGone() {
   scoped_refptr<RenderFrameDevToolsAgentHost> protect(this);
   if (IsAttached())
     RevokePolicy();
  ForceDetachAllSessions();
   frame_host_ = nullptr;
   agent_ptr_.reset();
   SetFrameTreeNode(nullptr);
  Release();
}

void RenderFrameDevToolsAgentHost::DestroyOnRenderFrameGone() {
   scoped_refptr<RenderFrameDevToolsAgentHost> protect(this);
   if (IsAttached())
     RevokePolicy();
  ForceDetachAllClients();
   frame_host_ = nullptr;
   agent_ptr_.reset();
   SetFrameTreeNode(nullptr);
  Release();
}
