Force context allocation for variables in generator scopes.

Force context allocation for variables in generator scopes.

* src/scopes.h (ForceContextAllocation, has_forced_context_allocation):
  New interface to force context allocation for an entire function's
  scope.

* src/scopes.cc: Unless a new scope is a function scope, if its outer
  scope has forced context allocation, it should also force context
  allocation.
  (MustAllocateInContext): Return true if the scope as a whole has
  forced context allocation.
  (CollectStackAndContextLocals): Allow temporaries to be
  context-allocated.

* src/parser.cc (ParseFunctionLiteral): Force context allocation for
  generator scopes.

* src/v8globals.h (VariableMode): Update comment on TEMPORARY.

* src/arm/full-codegen-arm.cc (Generate):
* src/ia32/full-codegen-ia32.cc (Generate):
* src/x64/full-codegen-x64.cc (Generate): Assert that generators have no
  stack slots.

* test/mjsunit/harmony/generators-instantiation.js: New test.

BUG=v8:2355
TEST=mjsunit/harmony/generators-instantiation

Review URL: https://codereview.chromium.org/13408005
Patch from Andy Wingo <wingo@igalia.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14152 ce2b1a6d-e550-0410-aec6-3dcde31c8c00