Port r14236 (7d56d7c5)

Original commit message:
* src/generator.js: Add methods and intialization for generator meta-objects.

* src/contexts.h:
* src/bootstrapper.cc (InitializeExperimentalGlobal): Make generator
  meta-objects, and store maps for constructing generator functions
  and their prototypes.

* src/factory.h:
* src/factory.cc (MapForNewFunction): New helper.
  (NewFunctionFromSharedFunctionInfo): Use the new helper.

* src/heap.cc (AllocateFunctionPrototype, AllocateInitialMap): For
   generators, allocate appropriate prototypes and maps.

* src/code-stubs.h:
* src/arm/code-stubs-arm.h:
* src/arm/full-codegen-arm.h:
* src/ia32/code-stubs-ia32.h:
* src/ia32/full-codegen-ia32.h:
* src/x64/code-stubs-x64.h:
* src/x64/full-codegen-x64.h: Allow fast closure creation for generators,
using the appropriate map.

* test/mjsunit/harmony/builtins.js: Add a special case for
  GeneratorFunctionPrototype.prototype.__proto__.

BUG=

Review URL: https://codereview.chromium.org/13988003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14238 ce2b1a6d-e550-0410-aec6-3dcde31c8c00