Add a HBreak instruction for debugging

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index 47ef40a8f51361e86e4aae37a354e99e915c3650..ae0d6283f44c1a483964506e5644fbabccbf5ea8 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -1827,6 +1827,11 @@ void LCodeGen::EmitBranchF(int left_block, int right_block,
 }
 
 
+void LCodeGen::DoDebugBreak(LDebugBreak* instr) {
+  __ stop("LDebugBreak");
+}
+
+
 void LCodeGen::DoBranch(LBranch* instr) {
   int true_block = chunk_->LookupDestination(instr->true_block_id());
   int false_block = chunk_->LookupDestination(instr->false_block_id());