Resynthesize deferred imports from Kernel.

R=brianwilkerson@google.com

Bug:
Change-Id: I6eca89aced40ccfca273152860dad2c5fdd3ddb5
Reviewed-on: https://dart-review.googlesource.com/5886
Reviewed-by: Paul Berry <paulberry@google.com>

pkg/analyzer/lib/src/dart/element/element.dart

@@ -5930,6 +5930,9 @@ class ImportElementImpl extends UriReferencedElementImpl
 
   @override
   bool get isDeferred {
+    if (_kernel != null) {
+      return _kernel.isDeferred;
+    }
     if (_unlinkedImport != null) {
       return _unlinkedImport.isDeferred;
     }

pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart

@@ -406,11 +406,6 @@ class ResynthesizeKernelStrongTest extends ResynthesizeTest {
     await super.test_import_configurations_useFirst();
   }
 
-  @failingTest
-  test_import_deferred() async {
-    await super.test_import_deferred();
-  }
-
   @failingTest
   test_import_invalidUri_metadata() async {
     await super.test_import_invalidUri_metadata();

pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart

@@ -771,9 +771,15 @@ class KernelLibraryBuilder
     for (Import import in imports) {
       Library importedLibrary = import.imported.target;
       if (importedLibrary != null) {
-        library.addDependency(new LibraryDependency.import(importedLibrary,
-            name: import.prefix,
-            combinators: toKernelCombinators(import.combinators)));
+        if (import.deferred && import.prefix != null) {
+          library.addDependency(new LibraryDependency.deferredImport(
+              importedLibrary, import.prefix,
+              combinators: toKernelCombinators(import.combinators)));
+        } else {
+          library.addDependency(new LibraryDependency.import(importedLibrary,
+              name: import.prefix,
+              combinators: toKernelCombinators(import.combinators)));
+        }
       }
     }