[turbofan] Improve testability of the InstructionSelector.

src/compiler/instruction-selector.cc

Index: src/compiler/instruction-selector.cc
diff --git a/src/compiler/instruction-selector.cc b/src/compiler/instruction-selector.cc
index 15ff73966b8507628c6d63ffa92e995435e1e35f..4cca17156298d8dfd6eb3e1adb2ea4aa83264518 100644
--- a/src/compiler/instruction-selector.cc
+++ b/src/compiler/instruction-selector.cc
@@ -14,10 +14,12 @@ namespace internal {
 namespace compiler {
 
 InstructionSelector::InstructionSelector(InstructionSequence* sequence,
-                                         SourcePositionTable* source_positions)
+                                         SourcePositionTable* source_positions,
+                                         Features features)
     : zone_(sequence->isolate()),
       sequence_(sequence),
       source_positions_(source_positions),
+      features_(features),
       current_block_(NULL),
       instructions_(InstructionDeque::allocator_type(zone())),
       defined_(graph()->NodeCount(), false, BoolVector::allocator_type(zone())),