Macro. Reuse parsed unit when merging macro results.

This saves another 160 ms.

Bug: #55784
Change-Id: If626d616999b85edaaa4028cbe5fc70fbc1bf86a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/372960
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/summary2/library_builder.dart

@@ -579,15 +579,11 @@ class LibraryBuilder with MacroApplicationsContainer {
     var importedAugmentation = importState.importedAugmentation!;
     var importedFile = importedAugmentation.file;
 
-    var unitNode = performance.run(
-      'importedFile.parse()',
-      (performance) {
-        performance.getDataInt('length').add(importedFile.content.length);
-        return importedFile.parse(
-          performance: performance,
-        );
-      },
+    var importedFileParsed = importedFile.getParsed(
+      performance: performance,
     );
+    var unitNode = importedFileParsed.unit;
+
     var unitElement = CompilationUnitElementImpl(
       source: importedFile.source,
       librarySource: importedFile.source,