[DevTools] InspectorFrontendHost implementation in DevTools app.

BUG=431697

Review URL: https://codereview.chromium.org/733053008

git-svn-id: svn://svn.chromium.org/blink/trunk@185766 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: follow up to SplitView shadow migration, fixing edge case styling in timeline panel.

TBR=apavlov
BUG=417275

Review URL: https://codereview.chromium.org/746893002

git-svn-id: svn://svn.chromium.org/blink/trunk@185772 bbb929c8-8fbe-4397-9dbb-9b2b20218538