dart2js cps: Use definitions by default, not references.

pkg/compiler/lib/src/cps_ir/gvn.dart

Index: pkg/compiler/lib/src/cps_ir/gvn.dart
diff --git a/pkg/compiler/lib/src/cps_ir/gvn.dart b/pkg/compiler/lib/src/cps_ir/gvn.dart
index 4d57744558b33062ce407edb853f1810a1579099..8bf896d907a1503aea69362c9f45c984148adfb4 100644
--- a/pkg/compiler/lib/src/cps_ir/gvn.dart
+++ b/pkg/compiler/lib/src/cps_ir/gvn.dart
@@ -403,7 +403,7 @@ class GVN extends TrampolineRecursiveVisitor implements Pass {
   }
 
   void visitInvokeContinuation(InvokeContinuation node) {
-    Continuation cont = node.continuation.definition;
+    Continuation cont = node.continuation;
     if (cont.isRecursive) return;
     EffectNumbers join = effectsAt[cont];
     if (join == null) {
@@ -414,8 +414,8 @@ class GVN extends TrampolineRecursiveVisitor implements Pass {
   }
 
   void visitBranch(Branch node) {
-    Continuation trueCont = node.trueContinuation.definition;
-    Continuation falseCont = node.falseContinuation.definition;
+    Continuation trueCont = node.trueContinuation;
+    Continuation falseCont = node.falseContinuation;
     // Copy the effect number vector once, so the analysis of one branch does
     // not influence the other.
     effectsAt[trueCont] = effectNumbers;