Disable mirror cache when initializing DebuggerScript.js

We never look up mirror object by its id. To avoid possible memory leaks caused by mirrors stuck in the cache we disable mirror cache completely.

This change depends on the ToggleMirrorCache added in V8 in https://code.google.com/p/v8/source/detail?r=21644

BUG=376534

Review URL: https://codereview.chromium.org/317963003

git-svn-id: svn://svn.chromium.org/blink/trunk@175642 bbb929c8-8fbe-4397-9dbb-9b2b20218538