Added 'dynamic' keyword, so that 'Dynamic' can be deprecated.

lib/compiler/implementation/dart_backend/placeholder_collector.dart

Index: lib/compiler/implementation/dart_backend/placeholder_collector.dart
diff --git a/lib/compiler/implementation/dart_backend/placeholder_collector.dart b/lib/compiler/implementation/dart_backend/placeholder_collector.dart
index d6bbd20682073f6808ac2c9830fa579ad3ce3603..381b5da132b309018184d307446b06854324bca4 100644
--- a/lib/compiler/implementation/dart_backend/placeholder_collector.dart
+++ b/lib/compiler/implementation/dart_backend/placeholder_collector.dart
@@ -422,7 +422,8 @@ class PlaceholderCollector extends Visitor {
   static bool isDynamicType(TypeAnnotation typeAnnotation) {
     if (!isPlainTypeName(typeAnnotation)) return false;
     String name = typeAnnotation.typeName.asIdentifier().source.slowToString();
-    return name == 'Dynamic';
+    // TODO(aprelev@gmail.com): Removed deprecated Dynamic keyword support.
+    return name == 'Dynamic' || name == 'dynamic';
   }
 
   visitTypeAnnotation(TypeAnnotation node) {