Insert checks before deferred calls and accesses.

sdk/lib/_internal/compiler/implementation/compile_time_constants.dart

Index: sdk/lib/_internal/compiler/implementation/compile_time_constants.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compile_time_constants.dart b/sdk/lib/_internal/compiler/implementation/compile_time_constants.dart
index 2dfbb57f492623e0aeaf3515e3a700386c895c8f..33576a4d100bff838babb9da78c5d39b3c6924e9 100644
--- a/sdk/lib/_internal/compiler/implementation/compile_time_constants.dart
+++ b/sdk/lib/_internal/compiler/implementation/compile_time_constants.dart
@@ -417,31 +417,9 @@ class CompileTimeConstantEvaluator extends Visitor {
   /// Returns true if the prefix of the send resolves to a deferred import
   /// prefix.
   bool isDeferredUse(Send send) {
-    // We handle:
-    // 1. Send(Send(Send(null, Prefix), className), staticName)
-    // 2. Send(Send(Prefix, Classname), staticName)
-    // 3. Send(Send(null, Prefix), staticName | className)
-    // 4. Send(Send(Prefix), staticName | className)
-    // Nodes of the forms 2,4 occur in metadata.
     if (send == null) return false;
-    while (send.receiver is Send) {
-      send = send.receiver;
-    }
-    Identifier prefixNode;
-    if (send.receiver is Identifier) {
-      prefixNode = send.receiver;
-    } else if (send.receiver == null &&
-        send.selector is Identifier) {
-      prefixNode = send.selector;
-    }
-    if (prefixNode != null) {
-      Element maybePrefix = elements[prefixNode.asIdentifier()];
-      if (maybePrefix != null && maybePrefix.isPrefix() &&
-          (maybePrefix as PrefixElement).isDeferred) {
-        return true;
-      }
-    }
-    return false;
+    return compiler.deferredLoadTask
+        .deferredPrefixElement(send, elements) != null;
   }
 
   Constant visitIdentifier(Identifier node) {