Improve and simplify removal of unreachable code

src/lithium.cc

Index: src/lithium.cc
diff --git a/src/lithium.cc b/src/lithium.cc
index fa837c7edef2fbbd23f5f7d9f983bd107b76998c..6a45d6c59d0e55d2076e539e61a5dcdbc802e4b7 100644
--- a/src/lithium.cc
+++ b/src/lithium.cc
@@ -490,6 +490,14 @@ void LChunk::set_allocated_double_registers(BitVector* allocated_registers) {
 }
 
 
+LInstruction* LChunkBuilder::CheckElideControlInstruction(
+    HControlInstruction* instr) {
+  HBasicBlock* successor;
+  if (!instr->KnownSuccessorBlock(&successor)) return NULL;
+  return new(zone()) LGoto(successor);
+}
+
+
 LPhase::~LPhase() {
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceLithium(name(), chunk_);