Fine. Skip unnamed extensions from 'structureMismatched'.

Unnamed extensions cannot be referenced in any way, even inside the same
library, in contrast to private named elements. We already skipped them
while adding items to the library manifests. However we recorded unnamed
extensions as `structureMismatchedCount`, which added noise.

No new test because nothing is affected outside.

Now, after changing a single public method in the analyzer: "(name:
computeManifests, count: 1, elapsed: 0:00:00.146594, elapsedSelf:
0:00:00.146594)(libraryCount: 275, structureMatchedCount: 33907,
structureMismatchedCount: 1, transitiveAffectedCount: 1,
transitiveMatchedCount: 33907)"

Change-Id: I7ab46bba1b0888f794889fe234d864a4d6a228fb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/447822
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/fine/library_manifest.dart

@@ -1161,8 +1161,10 @@ class _LibraryMatch {
             structureMismatched.add(element);
           }
         case ExtensionElementImpl():
-          if (!_matchExtension(name: name, element: element)) {
-            structureMismatched.add(element);
+          if (name != null) {
+            if (!_matchExtension(name: name, element: element)) {
+              structureMismatched.add(element);
+            }
           }
         case ExtensionTypeElementImpl():
           if (!_matchExtensionType(name: name, element: element)) {