Clean up imports and exports.

Each layer is supposed to reexport the parts of the previous layer
that are part of its API.

- In painting.dart, export from dart:ui all the Canvas-related APIs
  that make sense to be used at higher levels, e.g. PaintingStyle.

- Delete painting/shadows.dart. It was dead code.

- In rendering/object.dart, export all of painting.dart.

- In widgets/basic.dart, export all of painting.dart and
  animation.dart. Some classes in animation/ are renamed to make this
  less disruptive and confusing to the namespace.

- Split out Stocks back into an import model rather than a part model,
  so that it's easier to manage its dependencies on a per-file basis.

- Move Ticker to scheduler library.

- Remove as many redundant imports as possible now.

- Some minor nit picking cleanup in various files.
diff --git a/examples/stocks/lib/main.dart b/examples/stocks/lib/main.dart
index 38fe498..c342b4e 100644
--- a/examples/stocks/lib/main.dart
+++ b/examples/stocks/lib/main.dart
@@ -5,29 +5,18 @@
 library stocks;
 
 import 'dart:async';
-import 'dart:collection';
-import 'dart:math' as math;
-import 'dart:ui' as ui;
 
-import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
-import 'package:flutter/painting.dart';
-import 'package:flutter/rendering.dart';
-import 'package:flutter/scheduler.dart';
+import 'package:flutter/rendering.dart' show debugPaintSizeEnabled;
 import 'package:intl/intl.dart';
 
-import 'stock_data.dart';
 import 'i18n/stock_messages_all.dart';
-
-part 'stock_arrow.dart';
-part 'stock_home.dart';
-part 'stock_list.dart';
-part 'stock_menu.dart';
-part 'stock_row.dart';
-part 'stock_settings.dart';
-part 'stock_strings.dart';
-part 'stock_symbol_viewer.dart';
-part 'stock_types.dart';
+import 'stock_data.dart';
+import 'stock_home.dart';
+import 'stock_settings.dart';
+import 'stock_strings.dart';
+import 'stock_symbol_viewer.dart';
+import 'stock_types.dart';
 
 class StocksApp extends StatefulComponent {
   StocksAppState createState() => new StocksAppState();
@@ -94,7 +83,7 @@
     return null;
   }
 
-  Future<LocaleQueryData> _onLocaleChanged(ui.Locale locale) async {
+  Future<LocaleQueryData> _onLocaleChanged(Locale locale) async {
     String localeString = locale.toString();
     await initializeMessages(localeString);
     Intl.defaultLocale = localeString;