DevTools: initial support of box selection on FlameChart

If shift is held when dragging starts on the flame chart rectangle selection box will be drawn for the selected region. Selected range duration will be printed at the left top corner of the rectangle with precision of 0.01 ms.

BUG=407113

Review URL: https://codereview.chromium.org/665423003

git-svn-id: svn://svn.chromium.org/blink/trunk@184194 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: fix nowrap style in the elements panel.

BUG=425976

Review URL: https://codereview.chromium.org/649633005

git-svn-id: svn://svn.chromium.org/blink/trunk@184196 bbb929c8-8fbe-4397-9dbb-9b2b20218538