Background compilation work:

runtime/vm/assembler_arm.cc

Index: runtime/vm/assembler_arm.cc
diff --git a/runtime/vm/assembler_arm.cc b/runtime/vm/assembler_arm.cc
index 6c016c9c21f64efcf27fc0305de4ca087c769d34..c86b2e9043d897a29566d90c1abc28a6051d77fa 100644
--- a/runtime/vm/assembler_arm.cc
+++ b/runtime/vm/assembler_arm.cc
@@ -1516,6 +1516,7 @@ void Assembler::LoadWordFromPoolOffset(Register rd,
 
 void Assembler::CheckCodePointer() {
 #ifdef DEBUG
+  Comment("CheckCodePointer");
   Label cid_ok, instructions_ok;
   Push(R0);
   Push(IP);
@@ -3252,6 +3253,7 @@ void Assembler::ReserveAlignedFrameSpace(intptr_t frame_space) {
 
 
 void Assembler::EnterCallRuntimeFrame(intptr_t frame_space) {
+  Comment("EnterCallRuntimeFrame");
   // Preserve volatile CPU registers and PP.
   EnterFrame(kDartVolatileCpuRegs | (1 << PP) | (1 << FP), 0);
   COMPILE_ASSERT((kDartVolatileCpuRegs & (1 << PP)) == 0);