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 7a33d97692815cf9fa685560c7dac7eac3a63bf4..277a411ea2b24186dcac0ec3d6c5ebebdfdfd919 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
@@ -1190,6 +1190,10 @@ class ConstantNamingVisitor implements ConstantVisitor {
   visitDummy(DummyConstant constant) {
     add('dummy_receiver');
   }
+
+  visitDeferred(DeferredConstant constant) {
+    addRoot('Deferred');
+  }
 }
 
 /**
@@ -1272,6 +1276,11 @@ 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);