Add a HBreak instruction for debugging

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 2b0f6118236d58ccf69d04fd28c3f4554cbb825c..96adb2f7b4bf2180d4963dc1ba88f9d24dea7d0e 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -2198,6 +2198,11 @@ void LCodeGen::EmitBranch(int left_block, int right_block, Condition cc) {
 }
 
 
+void LCodeGen::DoDebugBreak(LDebugBreak* instr) {
+  __ stop("LBreak");
+}
+
+
 void LCodeGen::DoBranch(LBranch* instr) {
   int true_block = chunk_->LookupDestination(instr->true_block_id());
   int false_block = chunk_->LookupDestination(instr->false_block_id());