Implements features to run "Hello, world!" on simulated MIPS.

runtime/vm/assembler_mips.cc

Index: runtime/vm/assembler_mips.cc
===================================================================
--- runtime/vm/assembler_mips.cc	(revision 21753)
+++ runtime/vm/assembler_mips.cc	(working copy)
@@ -12,6 +12,7 @@
 
 namespace dart {
 
+DECLARE_FLAG(bool, trace_sim);
 DEFINE_FLAG(bool, print_stop_message, false, "Print stop message.");
 
 
@@ -543,6 +544,18 @@
   break_(Instr::kStopMessageCode);
 }
 
+
+void Assembler::TraceSimMsg(const char* message) {
+  //  Don't bother adding in the messages unless tracing is enabled.
+  if (FLAG_trace_sim) {
+    Label msg;
+    b(&msg);
+    Emit(reinterpret_cast<int32_t>(message));
+    Bind(&msg);
+    break_(Instr::kMsgMessageCode);
+  }
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS