Test for LibraryElement.hasExtUri resynth.

[email protected]
BUG=

Review URL: https://codereview.chromium.org/1578263003 .

Author: scheglov

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

@@ -49,6 +49,7 @@ class ResynthTest extends ResolverTestCase {
     expect(resynthesized.displayName, original.displayName);
     expect(original.enclosingElement, isNull);
     expect(resynthesized.enclosingElement, isNull);
+    expect(resynthesized.hasExtUri, original.hasExtUri);
     compareCompilationUnitElements(resynthesized.definingCompilationUnit,
         original.definingCompilationUnit);
     expect(resynthesized.parts.length, original.parts.length);
@@ -486,6 +487,10 @@ class ResynthTest extends ResolverTestCase {
     // TODO(paulberry): test initializer
   }
 
+  fail_library_hasExtUri() {
+    checkLibrary('import "dart-ext:doesNotExist.dart";');
+  }
+
   LibraryElementImpl resynthesizeLibrary(
       Source source, LibraryElementImpl original, bool allowErrors,
       {int resynthesisCount: 1}) {