This patch implements optimized objectInfo structure which manages the set of observers associated with an object and the changeRecord types which they accept.

Observation in the normal case (Object.observe, default accept types, one observer) now allocates fewer objects and unobservation no longer needs to scan and splice an InternalArray -- making the combined speed of observe/unobserve about 200% faster.

This patch implements the following optimizations:

-objectInfo is initially created without any connected objects or arrays. The first observer is referenced directly by objectInfo, and when a second observer is added, changeObservers converts to a mapping of callbackPriority->observer, which allows for constant time registration/de-registration.

-observer.accept and objectInfo.performing are conceptually the same data-structure. This is now directly represented as an abstract "TypeMap" which can later be optimized to be a smi in common cases, (e.g:   https://codereview.chromium.org/19269007/).

-objectInfo observers are only represented by an object with an accept typeMap if the set of accept types is non-default

R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/19541010

Patch from Rafael Weinstein <rafaelw@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16629 ce2b1a6d-e550-0410-aec6-3dcde31c8c00