Fix equality between subclasses of Source

pkg/analyzer/test/src/context/context_test.dart

Index: pkg/analyzer/test/src/context/context_test.dart
diff --git a/pkg/analyzer/test/src/context/context_test.dart b/pkg/analyzer/test/src/context/context_test.dart
index ea41470e1737046d26d206d8d77cc36484d646f6..2258d4cb8c75734de11508015b1a1a7b75641c8e 100644
--- a/pkg/analyzer/test/src/context/context_test.dart
+++ b/pkg/analyzer/test/src/context/context_test.dart
@@ -2438,16 +2438,24 @@ int a = 0;''');
    * Perform analysis tasks up to 512 times and assert that it was enough.
    */
   void _analyzeAll_assertFinished([int maxIterations = 512]) {
+    bool finishedAnalyzing = false;
     for (int i = 0; i < maxIterations; i++) {
       List<ChangeNotice> notice = context.performAnalysisTask().changeNotices;
       if (notice == null) {
+        finishedAnalyzing = true;
         bool inconsistent = context.validateCacheConsistency();
         if (!inconsistent) {
           return;
         }
       }
     }
-    fail("performAnalysisTask failed to terminate after analyzing all sources");
+    if (finishedAnalyzing) {
+      fail(
+          "performAnalysisTask failed to finish analyzing all sources after $maxIterations iterations");
+    } else {
+      fail(
+          "performAnalysisTask failed to terminate after analyzing all sources");
+    }
   }
 
   void _assertNoExceptions() {