Add LoadTaggedClassIdMayBeSmi to assembly and improve performance of inline cache stubs.

runtime/vm/flow_graph_compiler_ia32.cc

Index: runtime/vm/flow_graph_compiler_ia32.cc
===================================================================
--- runtime/vm/flow_graph_compiler_ia32.cc	(revision 37007)
+++ runtime/vm/flow_graph_compiler_ia32.cc	(working copy)
@@ -1279,17 +1279,10 @@
   ASSERT(!arguments_descriptor.IsNull() && (arguments_descriptor.Length() > 0));
   const MegamorphicCache& cache =
       MegamorphicCache::ZoneHandle(table->Lookup(name, arguments_descriptor));
-  Label not_smi, load_cache;
+  Label load_cache;
   __ movl(EAX, Address(ESP, (argument_count - 1) * kWordSize));
-  __ testl(EAX, Immediate(kSmiTagMask));
-  __ j(NOT_ZERO, &not_smi, Assembler::kNearJump);
-  __ movl(EAX, Immediate(Smi::RawValue(kSmiCid)));
-  __ jmp(&load_cache);
+  __ LoadTaggedClassIdMayBeSmi(EAX, EAX);
 
-  __ Bind(&not_smi);
-  __ LoadClassId(EAX, EAX);
-  __ SmiTag(EAX);
-
   // EAX: class ID of the receiver (smi).
   __ Bind(&load_cache);
   __ LoadObject(EBX, cache);