Simplify generated code for object allocation with type arguments.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
===================================================================
--- runtime/vm/intermediate_language.cc	(revision 32653)
+++ runtime/vm/intermediate_language.cc	(working copy)
@@ -33,6 +33,7 @@
 DECLARE_FLAG(bool, trace_optimization);
 DECLARE_FLAG(bool, trace_constant_propagation);
 DECLARE_FLAG(bool, throw_on_javascript_int_overflow);
+DECLARE_FLAG(bool, enable_type_checks);
 
 Definition::Definition()
     : range_(NULL),
@@ -1498,6 +1499,11 @@
 }
 
 
+Definition* InstantiateTypeArgumentsInstr::Canonicalize(FlowGraph* flow_graph) {
+  return (FLAG_enable_type_checks || HasUses()) ? this : NULL;
+}
+
+
 LocationSummary* DebugStepCheckInstr::MakeLocationSummary(bool opt) const {
   const intptr_t kNumInputs = 0;
   const intptr_t kNumTemps = 0;