Clean up ARM assembly code loading and storing from/to a large offset.

runtime/vm/assembler_arm.h

Index: runtime/vm/assembler_arm.h
===================================================================
--- runtime/vm/assembler_arm.h	(revision 19530)
+++ runtime/vm/assembler_arm.h	(working copy)
@@ -259,8 +259,12 @@
     encoding_ = so.encoding() | am | (static_cast<uint32_t>(rn) << kRnShift);
   }
 
-  static bool CanHoldLoadOffset(LoadOperandType type, int offset);
-  static bool CanHoldStoreOffset(StoreOperandType type, int offset);
+  static bool CanHoldLoadOffset(LoadOperandType type,
+                                int32_t offset,
+                                int32_t* offset_mask);
+  static bool CanHoldStoreOffset(StoreOperandType type,
+                                 int32_t offset,
+                                 int32_t* offset_mask);
 
  private:
   uint32_t encoding() const { return encoding_; }