Implement representation selection as part of SimplifiedLowering. Representation selection also req…

src/compiler/lowering-builder.cc

Index: src/compiler/lowering-builder.cc
diff --git a/src/compiler/lowering-builder.cc b/src/compiler/lowering-builder.cc
index f3644cfef24a8a4bc31181f82285be36e5ba9d43..1246f54f147761cad7e240050e15ec9bba8a33cc 100644
--- a/src/compiler/lowering-builder.cc
+++ b/src/compiler/lowering-builder.cc
@@ -16,8 +16,12 @@ class LoweringBuilder::NodeVisitor : public NullNodeVisitor {
   explicit NodeVisitor(LoweringBuilder* lowering) : lowering_(lowering) {}
 
   GenericGraphVisit::Control Post(Node* node) {
-    SourcePositionTable::Scope pos(lowering_->source_positions_, node);
-    lowering_->Lower(node);
+    if (lowering_->source_positions_ != NULL) {
+      SourcePositionTable::Scope pos(lowering_->source_positions_, node);
+      lowering_->Lower(node);
+    } else {
+      lowering_->Lower(node);
+    }
     return GenericGraphVisit::CONTINUE;
   }