Fix logic in RenderPadding.

sky/tests/raw/box_layout-expected.txt

Index: sky/tests/raw/box_layout-expected.txt
diff --git a/sky/tests/raw/render_box-expected.txt b/sky/tests/raw/box_layout-expected.txt
similarity index 56%
copy from sky/tests/raw/render_box-expected.txt
copy to sky/tests/raw/box_layout-expected.txt
index 63daffb92e380655f85ed3b647b6020eab740eb9..511893d78a0931432463f3b4bf711c4b1d216699 100644
--- a/sky/tests/raw/render_box-expected.txt
+++ b/sky/tests/raw/box_layout-expected.txt
@@ -5,9 +5,14 @@ PAINT FOR FRAME #1 ----------------------------------------------
 1 | TestDisplayList() constructor: 800.0 x 600.0
 1 | paintChild at 0.0,0.0
 1 |  | TestDisplayList() constructor: 800.0 x 600.0
-1 |  | drawRect(0.0:0.0:600.0:800.0, Paint(0xff00ff00))
+1 |  | drawRect(0.0:0.0:600.0:800.0, Paint(0xff0000ff))
+1 |  | paintChild at 0.0,0.0
+1 |  |  | TestDisplayList() constructor: 800.0 x 600.0
+1 |  |  | paintChild at 50.0,50.0
+1 |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+1 |  |  |  | drawRect(0.0:0.0:100.0:700.0, Paint(0xff00ff00))
 ------------------------------------------------------------------------
-CONSOLE: PASS: should size to render view
+CONSOLE: PASS: padding
 CONSOLE: 
 CONSOLE: All 1 tests passed.
 CONSOLE: unittest-suite-success