Cleanup deoptimization code to make it architecture independent (in progress).

runtime/vm/instructions_arm.h

Index: runtime/vm/instructions_arm.h
===================================================================
--- runtime/vm/instructions_arm.h	(revision 22345)
+++ runtime/vm/instructions_arm.h	(working copy)
@@ -25,6 +25,12 @@
   uword TargetAddress() const;
   void SetTargetAddress(uword target_address) const;
 
+  // This constant length is only valid for inserted call patterns used for
+  // lazy deoptimization. Regular call pattern may vary in length.
+  static const int kFixedLengthInBytes = 3 * Instr::kInstrSize;
+
+  static void InsertAt(uword pc, uword target_address);
+
  private:
   uword Back(int n) const;
   int DecodeLoadObject(int end, Register* reg, Object* obj);