Avoid inlining constants that are used via a deferred import.

sdk/lib/_internal/compiler/implementation/js_backend/namer.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
index a652c7c8efbe26fccf433f230d99170c82a45521..db55415182e84b9ad8f634441a81c8e36507756f 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
@@ -1163,6 +1163,10 @@ class ConstantNamingVisitor implements ConstantVisitor {
   visitDummy(DummyConstant constant) {
     add('dummy_receiver');
   }
+
+  visitDeferred(DeferredConstant constant) {
+    addRoot('Deferred');
+  }
 }
 
 /**
@@ -1245,6 +1249,11 @@ class ConstantCanonicalHasher implements ConstantVisitor<int> {
         'DummyReceiverConstant should never be named and never be subconstant');
   }
 
+  visitDeferred(DeferredConstant constant) {
+    int hash = constant.prefix.hashCode;
+    return _combine(hash, constant.referenced.accept(this));
+  }
+
   int _hashString(int hash, String s) {
     int length = s.length;
     hash = _combine(hash, length);