Implement search for PrefixElement.

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

Index: pkg/analyzer/test/src/dart/analysis/search_test.dart
diff --git a/pkg/analyzer/test/src/dart/analysis/search_test.dart b/pkg/analyzer/test/src/dart/analysis/search_test.dart
index 8872ebd28c6c8ac2d7cf3f217c42ff1d728e8d59..e473ffc15d4b64fa589c9faed7731e3c3ce72665 100644
--- a/pkg/analyzer/test/src/dart/analysis/search_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/search_test.dart
@@ -38,6 +38,7 @@ class ExpectedResult {
         result.isResolved == this.isResolved &&
         result.isQualified == this.isQualified &&
         result.offset == this.offset &&
+        result.length == this.length &&
         result.enclosingElement == this.enclosingElement;
   }
 
@@ -510,6 +511,34 @@ main() {
     await _verifyReferences(element, expected);
   }
 
+  test_searchReferences_PrefixElement() async {
+    String partCode = r'''
+part of my_lib;
+ppp.Future c;
+''';
+    provider.newFile(_p('$testProject/my_part.dart'), partCode);
+    await _resolveTestUnit('''
+library my_lib;
+import 'dart:async' as ppp;
+part 'my_part.dart';
+main() {
+  ppp.Future a;
+  ppp.Stream b;
+}
+''');
+    PrefixElement element = _findElementAtString('ppp;');
+    Element a = _findElement('a');
+    Element b = _findElement('b');
+    Element c = findChildElement(testLibraryElement, 'c');
+    var expected = [
+      _expectId(a, SearchResultKind.REFERENCE, 'ppp.Future'),
+      _expectId(b, SearchResultKind.REFERENCE, 'ppp.Stream'),
+      new ExpectedResult(c, SearchResultKind.REFERENCE,
+          partCode.indexOf('ppp.Future c'), 'ppp'.length)
+    ];
+    await _verifyReferences(element, expected);
+  }
+
   test_searchReferences_PropertyAccessorElement_getter() async {
     await _resolveTestUnit('''
 class A {