VM: Array bounds checks that don't deoptimize for precompiled code.

runtime/vm/assembler_ia32.h

Index: runtime/vm/assembler_ia32.h
diff --git a/runtime/vm/assembler_ia32.h b/runtime/vm/assembler_ia32.h
index d777b9b19c18e51187fe304b83dca5529f3cb3d0..df3d6ff8cb1b8f1074cb254a6fe1cb41ae840034 100644
--- a/runtime/vm/assembler_ia32.h
+++ b/runtime/vm/assembler_ia32.h
@@ -767,6 +767,11 @@ class Assembler : public ValueObject {
     sarl(reg, Immediate(kSmiTagSize));
   }
 
+  void BranchIfNotSmi(Register reg, Label* label) {
+    testl(reg, Immediate(kSmiTagMask));
+    j(NOT_ZERO, label);
+  }
+
   void Align(intptr_t alignment, intptr_t offset);
   void Bind(Label* label);
   void Jump(Label* label) { jmp(label); }