Constants! Constants everywhere! (#9286)

Aggressively apply the const lint.

examples/layers/widgets/styled_text.dart

diff --git a/examples/layers/widgets/styled_text.dart b/examples/layers/widgets/styled_text.dart
index e151da3..917bc0e 100644
--- a/examples/layers/widgets/styled_text.dart
+++ b/examples/layers/widgets/styled_text.dart
@@ -124,7 +124,7 @@
     theme: new ThemeData.light(),
     home: new Scaffold(
       appBar: new AppBar(
-        title: new Text('Hal and Dave')
+        title: const Text('Hal and Dave')
       ),
       body: new Material(
         color: Colors.grey.shade50,