DevTools: Refactor the way workspace is populated.

In particular:
 - Renamed workspace providers to workspace bindings.
 - Migrated ProjectDelegate events to ProjectStore methods.

R=pfeldman

Review URL: https://codereview.chromium.org/231233002

git-svn-id: svn://svn.chromium.org/blink/trunk@171250 bbb929c8-8fbe-4397-9dbb-9b2b20218538