Adds native/leaf runtime call stub and redirection on MIPS.

runtime/vm/assembler_mips.h

Index: runtime/vm/assembler_mips.h
===================================================================
--- runtime/vm/assembler_mips.h	(revision 20794)
+++ runtime/vm/assembler_mips.h	(working copy)
@@ -515,6 +515,14 @@
     jr(TMP);
   }
 
+  void BranchPatchable(const ExternalLabel* label) {
+    const uint16_t low = Utils::Low16Bits(label->address());
+    const uint16_t high = Utils::High16Bits(label->address());
+    lui(TMP, Immediate(high));
+    ori(TMP, TMP, Immediate(low));
+    jr(TMP);
+  }

[regis, 2013/04/02 20:16:03]

Ah, it is back :-)
But you should make the delay slot unavailable if you want to guarantee a fixed
code sequence length.

[zra, 2013/04/02 20:24:40]

Done.

+
   void BranchLink(const ExternalLabel* label) {
     LoadImmediate(TMP, label->address());
     jalr(TMP);