Remove ScriptState from IndexedDB code

This CL removes almost all ScriptStates from IndexedDB code by replacing them with ExecutionContext. (NewScriptState is not needed. ExecutionContext is enough.)

BUG=357144

Review URL: https://codereview.chromium.org/238583003

git-svn-id: svn://svn.chromium.org/blink/trunk@171553 bbb929c8-8fbe-4397-9dbb-9b2b20218538