Implements OSR for arm and mips.

runtime/vm/assembler_arm.h

Index: runtime/vm/assembler_arm.h
===================================================================
--- runtime/vm/assembler_arm.h	(revision 24893)
+++ runtime/vm/assembler_arm.h	(working copy)
@@ -665,6 +665,11 @@
   void EnterDartFrame(intptr_t frame_size);
   void LeaveDartFrame();
 
+  // Set up a Dart frame for a function compiled for on-stack replacement.
+  // The frame layout is a normal Dart frame, but the frame is partially set
+  // up on entry (it is the frame of the unoptimized code).
+  void EnterOsrFrame(intptr_t extra_size);
+
   // Set up a stub frame so that the stack traversal code can easily identify
   // a stub frame.
   void EnterStubFrame(bool uses_pp = false);