DevTools: Page.navigate response should contain a frameId.

BUG=375205
NOTRY=true

Review URL: https://codereview.chromium.org/362503003

git-svn-id: svn://svn.chromium.org/blink/trunk@177224 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Make target in ProfileHeader nullable, because it could be created from file

BUG=

Review URL: https://codereview.chromium.org/359313002

git-svn-id: svn://svn.chromium.org/blink/trunk@177225 bbb929c8-8fbe-4397-9dbb-9b2b20218538