Add some basic tests for the material buttons

sky/tests/widgets/buttons-expected.txt

Index: sky/tests/widgets/buttons-expected.txt
diff --git a/sky/tests/widgets/buttons-expected.txt b/sky/tests/widgets/buttons-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..1ae64e7914eeb736602a129e91ff7b0f82fc4d24
--- /dev/null
+++ b/sky/tests/widgets/buttons-expected.txt
@@ -0,0 +1,50 @@
+CONSOLE: TestRenderView enabled
+CONSOLE: 
+PAINT FOR FRAME #1 ----------------------------------------------
+1 | TestDisplayList() constructor: 800.0 x 600.0
+------------------------------------------------------------------------
+CONSOLE: 
+PAINT FOR FRAME #2 ----------------------------------------------
+2 | TestDisplayList() constructor: 800.0 x 600.0
+2 | paintChild RenderPositionedBox at Point(0.0, 0.0)
+2 |  | TestDisplayList() constructor: 800.0 x 600.0
+2 |  | paintChild RenderPadding at Point(348.0, 274.0)
+2 |  |  | TestDisplayList() constructor: 800.0 x 600.0
+2 |  |  | paintChild RenderConstrainedBox at Point(8.0, 8.0)
+2 |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+2 |  |  |  | drawRRect(Instance of 'RRect', Paint(Color(0xffe0e0e0)))
+2 |  |  |  | paintChild RenderPositionedBox at Point(8.0, 0.0)
+2 |  |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+2 |  |  |  |  | paintChild RenderParagraph at Point(6.0, 10.0)
+2 |  |  |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+------------------------------------------------------------------------
+CONSOLE: 
+PAINT FOR FRAME #3 ----------------------------------------------
+3 | TestDisplayList() constructor: 800.0 x 600.0
+3 | paintChild RenderPositionedBox at Point(0.0, 0.0)
+3 |  | TestDisplayList() constructor: 800.0 x 600.0
+3 |  | paintChild RenderPadding at Point(348.0, 274.0)
+3 |  |  | TestDisplayList() constructor: 800.0 x 600.0
+3 |  |  | paintChild RenderConstrainedBox at Point(8.0, 8.0)
+3 |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+3 |  |  |  | drawRRect(Instance of 'RRect', Paint(Color(0xfffafafa)))
+3 |  |  |  | paintChild RenderPositionedBox at Point(8.0, 0.0)
+3 |  |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+3 |  |  |  |  | paintChild RenderParagraph at Point(6.0, 10.0)
+3 |  |  |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+------------------------------------------------------------------------
+CONSOLE: 
+PAINT FOR FRAME #4 ----------------------------------------------
+4 | TestDisplayList() constructor: 800.0 x 600.0
+4 | paintChild RenderPositionedBox at Point(0.0, 0.0)
+4 |  | TestDisplayList() constructor: 800.0 x 600.0
+4 |  | paintChild RenderDecoratedBox at Point(372.0, 272.0)
+4 |  |  | TestDisplayList() constructor: 800.0 x 600.0
+4 |  |  | drawCircle(28.0, 28.0, 28.0, Paint(Color(0xfff44336)))
+4 |  |  | saveLayer(Rect.fromLTRB(0.0, 0.0, 56.0, 56.0), Paint(Color(0xff000000)))
+4 |  |  | clipPath(Instance of 'Path')
+4 |  |  | paintChild RenderParagraph at Point(22.0, 20.0)
+4 |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+4 |  |  | restore
+------------------------------------------------------------------------
+PAINTED 4 FRAMES