Iterate over PcDescriptors only via iterators, not via an index. (preparation for more compression …

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 38030)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -3884,7 +3884,7 @@
 class DebugStepCheckInstr : public TemplateInstruction<0> {
  public:
   DebugStepCheckInstr(intptr_t token_pos,
-                      PcDescriptors::Kind stub_kind)
+                      RawPcDescriptors::Kind stub_kind)
       : token_pos_(token_pos),
         stub_kind_(stub_kind) {
   }
@@ -3900,7 +3900,7 @@
 
  private:
   const intptr_t token_pos_;
-  const PcDescriptors::Kind stub_kind_;
+  const RawPcDescriptors::Kind stub_kind_;
 
   DISALLOW_COPY_AND_ASSIGN(DebugStepCheckInstr);
 };