Compute assigned variables and dominance frontiers.

runtime/vm/scopes.h

Index: runtime/vm/scopes.h
diff --git a/runtime/vm/scopes.h b/runtime/vm/scopes.h
index 3079e1e17f307f6f8acc234106d46e70d23cc02d..9a841ae3d83ba53569ef2da7ec0898e9c41a3131 100644
--- a/runtime/vm/scopes.h
+++ b/runtime/vm/scopes.h
@@ -58,10 +58,7 @@ class LocalVariable : public ZoneAllocated {
     return index_;
   }
 
-  // Assign an index to a local.  This function can be called more than once
-  // on the same on local (e.g., if we tried to compile in one mode, bailed
-  // out, and fell back to a different compilation mode).  In any case, it
-  // should not change the index once set.
+  // Assign an index to a local.
   void set_index(int index) {
     ASSERT(!HasIndex());
     ASSERT(index != kUnitializedIndex);