Don't add imports/exports elements for invalid URIs, with null Source.

pkg/analyzer/test/src/dart/analysis/driver_test.dart

Index: pkg/analyzer/test/src/dart/analysis/driver_test.dart
diff --git a/pkg/analyzer/test/src/dart/analysis/driver_test.dart b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
index 879a8e39a0efff346a629da51e2b9492b7d29978..1057800c09f11699dbd9acaa462834f97dd0d54b 100644
--- a/pkg/analyzer/test/src/dart/analysis/driver_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
@@ -504,6 +504,40 @@ class B extends A {
     expect(_getClassMethodReturnType(result.unit, 'B', 'm'), 'int');
   }
 
+  test_getResult_invalidUri_exports_dart() async {
+    String content = r'''
+export 'dart:async';
+export 'dart:noSuchLib';
+export 'dart:math';
+''';
+    _addTestFile(content, priority: true);
+
+    AnalysisResult result = await driver.getResult(testFile);
+    expect(result.path, testFile);
+    // Has only exports for valid URIs.
+    List<ExportElement> imports = result.unit.element.library.exports;
+    expect(
+        imports.map((import) => import.exportedLibrary.source.uri.toString()),
+        unorderedEquals(['dart:async', 'dart:math']));
+  }
+
+  test_getResult_invalidUri_imports_dart() async {
+    String content = r'''
+import 'dart:async';
+import 'dart:noSuchLib';
+import 'dart:math';
+''';
+    _addTestFile(content, priority: true);
+
+    AnalysisResult result = await driver.getResult(testFile);
+    expect(result.path, testFile);
+    // Has only imports for valid URIs.
+    List<ImportElement> imports = result.unit.element.library.imports;
+    expect(
+        imports.map((import) => import.importedLibrary.source.uri.toString()),
+        unorderedEquals(['dart:async', 'dart:math', 'dart:core']));
+  }
+
   test_getResult_mix_fileAndPackageUris() async {
     var a = _p('/test/bin/a.dart');
     var b = _p('/test/bin/b.dart');