Support scalar lists in array bounds check elimination.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 16697)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -4106,12 +4106,14 @@
 
   bool IsRedundant(RangeBoundary length);
 
+  // Returns the length offset for array and string types.
+  static intptr_t LengthOffsetFor(intptr_t class_id);
+
+  static bool IsFixedLengthArrayType(intptr_t class_id);
+
  private:
   intptr_t array_type_;
 
-  // Returns the length offset for array and string types.
-  static intptr_t LengthOffsetFor(intptr_t class_id);
-
   DISALLOW_COPY_AND_ASSIGN(CheckArrayBoundInstr);
 };