Reenable GVN for fields.

lib/compiler/implementation/ssa/nodes.dart

Index: lib/compiler/implementation/ssa/nodes.dart
diff --git a/lib/compiler/implementation/ssa/nodes.dart b/lib/compiler/implementation/ssa/nodes.dart
index 9d7ed244a63e0eefadbe46eba9092e0e2b3a97aa..139bc118e7f7e8d02156fbb21a450486c4f7b4aa 100644
--- a/lib/compiler/implementation/ssa/nodes.dart
+++ b/lib/compiler/implementation/ssa/nodes.dart
@@ -1272,7 +1272,9 @@ class HInvokeInterceptor extends HInvokeStatic {
 
   void prepareGvn() {
     if (isLengthGetterOnStringOrArray()) {
+      setUseGvn();
       clearAllSideEffects();
+      setDependsOnSomething();
     } else {
       setAllSideEffects();
     }
@@ -1303,7 +1305,9 @@ class HFieldGet extends HFieldAccess {
   accept(HVisitor visitor) => visitor.visitFieldGet(this);
 
   void prepareGvn() {
+    setUseGvn();
     clearAllSideEffects();

[floitsch, 2012/07/20 18:25:20]

The original version (when GVN was enabled) did not have the
"clearAllSideEffects()" call. Please confirm that it is correct to keep it.

+    if (!isFinalOrConst) setDependsOnSomething();
   }
 
   int typeCode() => 27;