Fix an off-by-one error in deoptimization compression.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index a23c441996e7b22607c342294641ceb3a6b2f5ef..5f19845b356c715f4c49ffb50ed5c14ffa542dee 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -2936,6 +2936,12 @@ class DeoptInfo : public Object {
   void ToInstructions(const Array& table,
                       GrowableArray<DeoptInstr*>* instructions) const;
 
+
+  // Returns true iff decompression yields the same instructions as the
+  // original.
+  bool VerifyDecompression(const GrowableArray<DeoptInstr*>& original,
+                           const Array& deopt_table) const;
+
  private:
   intptr_t* EntryAddr(intptr_t index, intptr_t entry_offset) const {
     ASSERT((index >=0) && (index < Length()));