Do not add values to HGraph in Lithium.

Lithium uses indexes after the maximium value ID in the HGraph as indexes
of virtual registers and assumes that the maximum value ID does not change.

The IsStandardConstant and GetConstantXX functions could add constants to
HGraph, which aliased virtual registers with real values. This could confuse
the register allocator to think that a value in a virtual register is tagged
and to incorrectly set it in the pointer map.

BUG=298269
TEST=mjsunit/regress/regress-298269.js
R=verwaest@chromium.org

Review URL: https://chromiumcodereview.appspot.com/66693002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17599 ce2b1a6d-e550-0410-aec6-3dcde31c8c00