Various cleanup/simplification in object-observe.js

Various cleanup/simplification in object-observe.js

The biggest change is the removal of the map wrapper objects:
we now operate directly on the observation weak map, since there
are already Get/GetOrCreate/Set functions for each info map.
Various other small cleanups as well, including the deletion of
unnecessary forwarding functions and making use of standard macros.

This is a reland of r24972, retaining GetObservationStateJS() to
keep snapshotting working properly.

R=rossberg@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=24990

[adamk, 2014-10-29 16:38:47]

adamk@chromium.org changed reviewers:
+ rossberg@chromium.org

[rossberg, 2014-10-29 17:22:27]

lgtm

[adamk, 2014-10-29 17:27:23]

Committed patchset #1 (id:1) manually as 24990 (presubmit successful).