Introduce V8HiddenValue

- r165735 removed V8HiddenPropertyName and it caused 6% performance regression in Indexed DB tests (https://code.google.com/p/chromium/issues/detail?id=338383)

- This CL essentially reverts r165735, although this CL is not a simple revert (because simple revert is no longer possible) but a revert with a couple of refactoring.

--- Rename V8HiddenPropertyName to V8HiddenValue.
--- Remove unnecessary hidden names from V8HiddenValue.h.
--- Make V8HiddenValue's methods better. Now V8HiddenValue has {get,set,delete}HiddenValue(), which is easy to understand.

- This CL will fix the performance regression in Indexed DB tests.

- In this CL, V8HiddenValue is still using SetHiddenValue/GetHiddenValue. In the next CL, I'll replace them with private names.

BUG=338383

Review URL: https://codereview.chromium.org/188513004

git-svn-id: svn://svn.chromium.org/blink/trunk@168678 bbb929c8-8fbe-4397-9dbb-9b2b20218538