DevTools: HeapProfiler can't save snapshot to the disk

After r179948 our heap profiler is unable to run
TempStorage shared worker because we have different
files layout in debug and release mode.

Unfortunatelly the existing schema of running dedicated
workers doesn't fit for shared workers due to
the difference in the workers API.

Also I found that there is a race between starting shared
worker and window.URL.revokeObjectURL(workerURL); call.

So I implemented plain simple Runtime.startSharedWorker
for our the only shared worker with the only script.

BUG=405007

Review URL: https://codereview.chromium.org/495073002

git-svn-id: svn://svn.chromium.org/blink/trunk@180737 bbb929c8-8fbe-4397-9dbb-9b2b20218538