Refactor string internalization.

Remove duplicate code in StringTable and Heap. Instead of having many InternalizeXXXString methods, add a general InternalizeStringWithKey that takes a string table key.

BUG=
R=dcarney@chromium.org, svenpanne@chromium.org

Review URL: https://codereview.chromium.org/140953002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18657 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix stub-invoked setter callback handling.

When invoking a setter callback for a property using
JSObject::SetPropertyWithCallback(),the callback arguments includes
a correct pair of receiver and holder objects.

Such a pair of _possibly different_ arguments (receiver, holder) must
also be supplied when invoking the same setter callback from JITed
code, when the setter is invoked through the StoreCallbackProperty
stub.

An example where this matters are the accessor properties kept on the
global scope of Worker (i.e., properties kept on the global object
itself, and not on its prototype.) Conflating the receiver with the
holder leads to general confusion when attempting to fetch out the
wrapper object.

LOG=N
R=dcarney@chromium.org, dcarney
BUG=239669

Review URL: https://codereview.chromium.org/139263008

Patch from Sigbjorn Finne <sigbjornf@opera.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18658 ce2b1a6d-e550-0410-aec6-3dcde31c8c00