Optimize AOT's switchable calls for the monomorphic case.

runtime/vm/instructions_arm_test.cc

Index: runtime/vm/instructions_arm_test.cc
diff --git a/runtime/vm/instructions_arm_test.cc b/runtime/vm/instructions_arm_test.cc
index de3ff6f4ab38bbddc285fc6157b93b5147d07a7d..24effd843e9c5f0ea22b9e6ae53296369de8db3d 100644
--- a/runtime/vm/instructions_arm_test.cc
+++ b/runtime/vm/instructions_arm_test.cc
@@ -27,8 +27,8 @@ ASSEMBLER_TEST_RUN(Call, test) {
   // The return address, which must be the address of an instruction contained
   // in the code, points to the Ret instruction above, i.e. one instruction
   // before the end of the code buffer.
-  CallPattern call(test->entry() + test->code().Size() - Instr::kInstrSize,
-                   test->code());
+  uword end = test->payload_start() + test->code().Size();
+  CallPattern call(end - Instr::kInstrSize, test->code());
   EXPECT_EQ(StubCode::InvokeDartCode_entry()->code(), call.TargetCode());
 }