Optimize AOT's switchable calls for the monomorphic case.

runtime/vm/assembler_mips.h

Index: runtime/vm/assembler_mips.h
diff --git a/runtime/vm/assembler_mips.h b/runtime/vm/assembler_mips.h
index 87717b656cdaec326d7fd12e563167a35dcbbbe7..095fa749869ff343b684d380879cfd59dc0498f7 100644
--- a/runtime/vm/assembler_mips.h
+++ b/runtime/vm/assembler_mips.h
@@ -243,7 +243,9 @@ class Assembler : public ValueObject {
         delay_slot_available_(false),
         in_delay_slot_(false),
         comments_(),
-        constant_pool_allowed_(true) { }
+        constant_pool_allowed_(true) {
+    MonomorphicCheckedEntry();
+  }
   ~Assembler() { }
 
   void PopRegister(Register r) { Pop(r); }
@@ -280,7 +282,6 @@ class Assembler : public ValueObject {
   }
 
   void set_use_far_branches(bool b) {
-    ASSERT(buffer_.Size() == 0);
     use_far_branches_ = b;
   }
 
@@ -295,6 +296,9 @@ class Assembler : public ValueObject {
   // the branch delay slot.
   void LeaveStubFrameAndReturn(Register ra = RA);
 
+  void NoMonomorphicCheckedEntry();
+  void MonomorphicCheckedEntry();
+
   void UpdateAllocationStats(intptr_t cid,
                              Register temp_reg,
                              Heap::Space space);