Replace start_env with initial_definitions in GraphEntryInstr.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 321e005eb5f8b8e6d186da1d1c581fc396d5bcd1..02b0dacfdcdc5bd0fae621e481a87339c2a702f7 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -138,12 +138,19 @@ GraphEntryInstr::GraphEntryInstr(TargetEntryInstr* normal_entry)
     : BlockEntryInstr(CatchClauseNode::kInvalidTryIndex),
       normal_entry_(normal_entry),
       catch_entries_(),
-      start_env_(NULL),
-      constant_null_(NULL),
+      initial_definitions_(),
       spill_slot_count_(0) {
 }
 
 
+ConstantInstr* GraphEntryInstr::constant_null() {
+  ASSERT(initial_definitions_.length() > 0 &&
+         initial_definitions_[0]->IsConstant() &&
+         initial_definitions_[0]->AsConstant()->value().IsNull());
+  return initial_definitions_[0]->AsConstant();
+}
+
+
 static bool CompareNames(const Library& lib,
                          const char* test_name,
                          const String& name) {