[frontend_server] do not run if full component is requested

Most of the time a hot restart will bail out due to the changed libraries,
but since the operation is pointless anyway it is better to short-circuit.

Change-Id: I86d3266f1502f612b0dd7cc6b7409c05bd7456c9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/165381
Reviewed-by: Alexander Aprelev <aam@google.com>
Commit-Queue: Jonah Williams <jonahwilliams@google.com>
diff --git a/pkg/frontend_server/lib/frontend_server.dart b/pkg/frontend_server/lib/frontend_server.dart
index 9e583c2..dc92143 100644
--- a/pkg/frontend_server/lib/frontend_server.dart
+++ b/pkg/frontend_server/lib/frontend_server.dart
@@ -1151,8 +1151,10 @@
   /// The resulting class name is written as a String to
   /// `_kernelBinaryFilename`.widget_cache, or else the file is deleted
   /// if it exists.
+  ///
+  /// Should not run if a full component is requested.
   void _updateWidgetCache(Component partialComponent) {
-    if (_widgetCache == null) {
+    if (_widgetCache == null || _generator.fullComponent) {
       return;
     }
     final String singleModifiedClassName =