[DevTools] Show reload warning when only user agent changed.

BUG=331324

Review URL: https://codereview.chromium.org/131923002

git-svn-id: svn://svn.chromium.org/blink/trunk@165208 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Remove no-op InspectorFrontendHost.close() and its clients

R=aandrey, eustas, loislo, yurys
NOTRY=true

Review URL: https://codereview.chromium.org/137343009

git-svn-id: svn://svn.chromium.org/blink/trunk@165209 bbb929c8-8fbe-4397-9dbb-9b2b20218538