DevTools: introduce object previews experiment

third_party/WebKit/LayoutTests/inspector/console/console-eval-scoped-expected.txt

 CONSOLE MESSAGE: line 4: with: Object property value
 CONSOLE MESSAGE: line 1: eval in with: Object property value
 CONSOLE MESSAGE: line 1: eval in function: Function parameter
 Tests that evaluating 'console.log()' in the console will have access to its outer scope variables. Bug 60547.
 
 
 Running: testSnippet1
 VM:4 with: Object property value
 VM:1 eval in with: Object property value
 
@@ skipping 55 matching lines @@
         className : "Object"
         description : "Object"
         objectId : <string>
         type : "object"
     }
     writable : true
 }
 
 Running: testGetEventListenersDoesNotThrow
 getEventListeners(document.body.firstChild)
-Object {}
+{}