Add a HBreak instruction for debugging

src/mips/lithium-mips.cc

Index: src/mips/lithium-mips.cc
diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index 719acb3b39e3f93ebe3139efc841cf5317d6cdaf..21963255899796d932daf8a6437ac75389b8c285 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -208,6 +208,10 @@ void LBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+LInstruction* LChunkBuilder::DoDebugBreak(HDebugBreak* instr) {
+  return new(zone()) LDebugBreak();
+}
+
 void LCmpIDAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if ");
   left()->PrintTo(stream);