Remove default monomorphic check code from functions and stubs that do not need it.

runtime/vm/assembler_arm64.cc

Index: runtime/vm/assembler_arm64.cc
diff --git a/runtime/vm/assembler_arm64.cc b/runtime/vm/assembler_arm64.cc
index 37e9ca3b59bd9031f33498a69ff6d942d3d59efa..33ab5279c1fc7ee86237b21a0a42ab560f117342 100644
--- a/runtime/vm/assembler_arm64.cc
+++ b/runtime/vm/assembler_arm64.cc
@@ -24,10 +24,10 @@ DEFINE_FLAG(bool, use_far_branches, false, "Always use far branches");
 Assembler::Assembler(bool use_far_branches)
     : buffer_(),
       prologue_offset_(-1),
+      has_single_entry_point_(true),
       use_far_branches_(use_far_branches),
       comments_(),
       constant_pool_allowed_(false) {
-  MonomorphicCheckedEntry();
 }
 
 
@@ -1238,18 +1238,10 @@ void Assembler::LeaveStubFrame() {
 }
 
 
-void Assembler::NoMonomorphicCheckedEntry() {
-  buffer_.Reset();
-  brk(0);
-  brk(0);
-  brk(0);
-  brk(0);
-  ASSERT(CodeSize() == Instructions::kCheckedEntryOffset);
-}
-
-
 // R0 receiver, R5 guarded cid as Smi
 void Assembler::MonomorphicCheckedEntry() {
+  ASSERT(has_single_entry_point_);
+  has_single_entry_point_ = false;
   bool saved_use_far_branches = use_far_branches();
   set_use_far_branches(false);