supress hint when using "show dynamic". This is a temporary fix to hide a hint

pkg/compiler/lib/src/library_loader.dart

Index: pkg/compiler/lib/src/library_loader.dart
diff --git a/pkg/compiler/lib/src/library_loader.dart b/pkg/compiler/lib/src/library_loader.dart
index 9caf929497f187d9dfbe50b2a1b65ee05318526f..e945e325eb3c3337d2d5c34568de5417acd58f5d 100644
--- a/pkg/compiler/lib/src/library_loader.dart
+++ b/pkg/compiler/lib/src/library_loader.dart
@@ -1335,7 +1335,10 @@ class LibraryDependencyNode {
             }
             reporter.reportHintMessage(identifier, MessageKind.EMPTY_HIDE,
                 {'uri': library.canonicalUri, 'name': name});
-          } else {
+          } else if (!library.isDartCore || name != 'dynamic') {
+            // TODO(sigmund): remove this condition, we don't report a hint for
+            // `import "dart:core" show dynamic;` until our tools match in
+            // semantics (see #29125).
             reporter.reportHintMessage(identifier, MessageKind.EMPTY_SHOW,
                 {'uri': library.canonicalUri, 'name': name});
           }