DevTools: Introduce WebInspector.Replaceable to fix module-wise compilation errors

R=aandrey, eustas, vsevik

Review URL: https://codereview.chromium.org/135043005

git-svn-id: svn://svn.chromium.org/blink/trunk@165228 bbb929c8-8fbe-4397-9dbb-9b2b20218538