Regression fix: HForceRepresentation shouldn't be an idef.

Instead, code sites that are interested in underlying constant integer values
should use HValue::IsInteger32Constant(). The issue is that the infer representation phase shouldn't "see through" HForceRepresentation nodes to an underlying, and less specific representation.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/65643003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17787 ce2b1a6d-e550-0410-aec6-3dcde31c8c00