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

runtime/vm/assembler_mips.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ASSEMBLER_MIPS_H_
 #define VM_ASSEMBLER_MIPS_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_mips.h directly; use assembler.h instead.
 #endif
@@ skipping 497 matching lines @@
     EmitRType(SPECIAL, rs, rt, rd, 0, XOR);
   }
 
   // Macros in alphabetical order.
 
   void Branch(const ExternalLabel* label) {
     LoadImmediate(TMP, label->address());
     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);
+    delay_slot()->nop();

[regis, 2013/04/02 20:40:51]

This works, but there is already a nop in the delay slot. This would be
clearer/simpler:
delay_slot_available_ = false;  // CodePatcher expects a nop.

+  }
+
   void BranchLink(const ExternalLabel* label) {
     LoadImmediate(TMP, label->address());
     jalr(TMP);
   }
 
   void BranchLinkPatchable(const ExternalLabel* label) {
     const int32_t offset =
         Array::data_offset() + 4*AddExternalLabel(label) - kHeapObjectTag;
     LoadWordFromPoolOffset(TMP, offset);
     jalr(TMP);
+    delay_slot()->nop();

[regis, 2013/04/02 20:40:51]

ditto

   }
 
   // If the signed value in rs is less than value, rd is 1, and 0 otherwise.
   void LessThanSImmediate(Register rd, Register rs, int32_t value) {
     LoadImmediate(TMP, value);
     slt(rd, rs, TMP);
   }
 
   // If the unsigned value in rs is less than value, rd is 1, and 0 otherwise.
   void LessThanUImmediate(Register rd, Register rs, uint32_t value) {
@@ skipping 179 matching lines @@
     delay_slot_available_ = true;
   }
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_MIPS_H_