Optimize AOT's switchable calls for the monomorphic case.

runtime/vm/disassembler_ia32.cc

Index: runtime/vm/disassembler_ia32.cc
diff --git a/runtime/vm/disassembler_ia32.cc b/runtime/vm/disassembler_ia32.cc
index 8f3d7f648e473a5c593bd487522cced0b44bc9a2..d0252d36114528d5e110f55677aa0f2c5a3be88d 100644
--- a/runtime/vm/disassembler_ia32.cc
+++ b/runtime/vm/disassembler_ia32.cc
@@ -1816,7 +1816,7 @@ void Disassembler::DecodeInstruction(char* hex_buffer, intptr_t hex_size,
   if (!code.IsNull() && code.is_alive()) {
     intptr_t offsets_length = code.pointer_offsets_length();
     for (intptr_t i = 0; i < offsets_length; i++) {
-      uword addr = code.GetPointerOffsetAt(i) + code.EntryPoint();
+      uword addr = code.GetPointerOffsetAt(i) + code.PayloadStart();
       if ((pc <= addr) && (addr < (pc + instruction_length))) {
         *object = &Object::Handle(*reinterpret_cast<RawObject**>(addr));
         break;