Measure time spent building graph of files.

pkg/front_end/lib/src/incremental_kernel_generator_impl.dart

Index: pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
diff --git a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
index d75a0fc7d25e13d750e189cd41b3b71caadb7d22..499e3fa70f8921c770e653756b2e672e57925aa4 100644
--- a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
+++ b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
@@ -93,7 +93,10 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
       await _refreshInvalidatedFiles();
 
       // Ensure that the graph starting at the entry point is ready.
-      FileState entryLibrary = await _fsState.getFile(_entryPoint);
+      FileState entryLibrary =
+          await _logger.runAsync('Build graph of files', () async {
+        return await _fsState.getFile(_entryPoint);
+      });
 
       List<LibraryCycle> cycles = _logger.run('Compute library cycles', () {
         List<LibraryCycle> cycles = entryLibrary.topologicalOrder;