DevTools: [JsDoc] Fix annotation errors detected by temporarily declaring WebInspector @const

R=eustas, vsevik

Review URL: https://codereview.chromium.org/100473017

git-svn-id: svn://svn.chromium.org/blink/trunk@164357 bbb929c8-8fbe-4397-9dbb-9b2b20218538