Issue 24277. Use node's offset as the source range start for the first unit node in Outline.

pkg/analysis_server/test/analysis/notification_outline_test.dart

Index: pkg/analysis_server/test/analysis/notification_outline_test.dart
diff --git a/pkg/analysis_server/test/analysis/notification_outline_test.dart b/pkg/analysis_server/test/analysis/notification_outline_test.dart
index 2d459acd691111e62d8707e16c1547c8ee496b43..fdac6b59c79d2a283bfba1e37f544be81725fc68 100644
--- a/pkg/analysis_server/test/analysis/notification_outline_test.dart
+++ b/pkg/analysis_server/test/analysis/notification_outline_test.dart
@@ -577,6 +577,8 @@ class A { // leftA
 
   test_sourceRange_inUnit() {
     addTestFile('''
+library lib;
+/// My first class.
 class A {
 } // endA
 class B {
@@ -593,7 +595,7 @@ class B {
         expect(element.kind, ElementKind.CLASS);
         expect(element.name, "A");
         {
-          int offset = 0;
+          int offset = testCode.indexOf("/// My first class.");
           int end = testCode.indexOf(" // endA");
           expect(outline.offset, offset);
           expect(outline.length, end - offset);