Support immediate operands for array bounds checks.

runtime/vm/locations.cc

Index: runtime/vm/locations.cc
===================================================================
--- runtime/vm/locations.cc	(revision 11818)
+++ runtime/vm/locations.cc	(working copy)
@@ -45,6 +45,22 @@
 }
 
 
+Location Location::RegisterOrConstant(Value* value) {
+  ConstantComp* constant = value->definition()->AsConstant();
+  return (constant != NULL)
+      ? Location::Constant(constant->value())
+      : Location::RequiresRegister();
+}
+
+
+Location Location::FixedRegisterOrConstant(Value* value, Register reg) {
+  ConstantComp* constant = value->definition()->AsConstant();
+  return (constant != NULL)
+      ? Location::Constant(constant->value())
+      : Location::RegisterLocation(reg);
+}
+
+
 const char* Location::Name() const {
   switch (kind()) {
     case kInvalid: return "?";