DevTools: Add context menu option for objects to save to temp variable.

Adding ability to access objects from printed ObjectPropertySections (console, scopes pane and etc.).

BUG=306120
R=pfeldman

Review URL: https://codereview.chromium.org/201613004

git-svn-id: svn://svn.chromium.org/blink/trunk@169649 bbb929c8-8fbe-4397-9dbb-9b2b20218538