Move sky/examples to sky/sdk/lib/example, and code changes to support that change. Fixes T277.

sky/sdk/lib/rendering/README.md

Index: sky/sdk/lib/rendering/README.md
diff --git a/sky/sdk/lib/rendering/README.md b/sky/sdk/lib/rendering/README.md
index bf1b7099f912e56a413513293874fdbf5d355939..e58f355e7b3e6ea08f0cc6223b4cc8f915e687d4 100644
--- a/sky/sdk/lib/rendering/README.md
+++ b/sky/sdk/lib/rendering/README.md
@@ -147,7 +147,7 @@ If you want to define a `RenderObject` that uses a new coordinate
 system, then you should inherit straight from `RenderObject`. Examples
 of doing this can be found in [`RenderBox`](box.dart), which deals in
 rectangles in cartesian space, and in the [sector_layout.dart
-example](../../../examples/rendering/sector_layout.dart), which
+example](../../../sdk/lib/example/rendering/sector_layout.dart), which
 implements a toy model based on polar coordinates. The `RenderView`
 class, which is used internally to adapt from the host system to this
 rendering framework, is another example.