Store pointer instead of reference to LocalVariable in ast and flow graph.

runtime/vm/scopes.cc

Index: runtime/vm/scopes.cc
===================================================================
--- runtime/vm/scopes.cc	(revision 10207)
+++ runtime/vm/scopes.cc	(working copy)
@@ -525,13 +525,13 @@
 }
 
 
-bool LocalVariable::Equals(const LocalVariable& other) const {
-  if (HasIndex() && other.HasIndex() && (index() == other.index())) {
-    if (is_captured() == other.is_captured()) {
+bool LocalVariable::Equals(const LocalVariable* other) const {
+  if (HasIndex() && other->HasIndex() && (index() == other->index())) {
+    if (is_captured() == other->is_captured()) {
       if (!is_captured()) {
         return true;
       }
-      if (owner()->context_level() == other.owner()->context_level()) {
+      if (owner()->context_level() == other->owner()->context_level()) {
         return true;
       }
     }