Fix e2e_test to work with current DDC output (#2626)

Fix e2e_test to work with current DDC output

Add a top level method and expect the result of calling that method in
an expression evaluation.

The existing test for expression evaluation in the context of a library
relied on the output of the `.toString()` of a top level method tearoff.
This representation changed recently causing the test to fail.

Author: nshahan

fixtures/_webdevSoundSmoke/web/main.dart

@@ -23,3 +23,5 @@ void main() {
     print('Counter is: ${++count}'); // Breakpoint: printCounter
   });
 }
+
+String topLevelMethod() => 'verify this!';

webdev/test/e2e_test.dart

@@ -382,15 +382,15 @@ void main() {
                   'valueAsString',
                   'Hello World!!'));
 
-          result =
-              await vmService.evaluate(isolateId, libraryId, 'main.toString()');
+          result = await vmService.evaluate(
+              isolateId, libraryId, 'topLevelMethod()');
 
           expect(
               result,
               const TypeMatcher<InstanceRef>().having(
                   (instance) => instance.valueAsString,
                   'valueAsString',
-                  contains('Closure: () => void')));
+                  equals('verify this!')));
         } finally {
           await vmService?.dispose();
           await exitWebdev(process);
@@ -555,7 +555,7 @@ void main() {
 
           expect(
               () =>
-                  vmService!.evaluate(isolateId, libraryId, 'main.toString()'),
+                  vmService!.evaluate(isolateId, libraryId, 'topLevelMethod()'),
               throwsRPCError);
         } finally {
           await vmService?.dispose();