Remove SampleApp and convert HelloWorld to sk_app

There is still a large amount of views code that could be trimmed down,
but which is used to implement samples (in viewer). Seemed simpler to
remove some of this code in pieces.

Bug: skia:
Change-Id: Ia3415060d03c8de604a154e3dc38379b754daab6
Reviewed-on: https://skia-review.googlesource.com/72801
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/tools/viewer/Viewer.h b/tools/viewer/Viewer.h
index f121c17..24f68b4 100644
--- a/tools/viewer/Viewer.h
+++ b/tools/viewer/Viewer.h
@@ -13,6 +13,7 @@
 #include "sk_app/Window.h"
 #include "gm.h"
 #include "SkAnimTimer.h"
+#include "SkJSONCPP.h"
 #include "SkTouchGesture.h"
 #include "Slide.h"