make GrPaint.h private -- IWYU

prerequisit: https://codereview.chromium.org/2743533002/

BUG=skia:

Change-Id: I8c2f34a6df165744ddeaeabb562cd6d6a9679b6a
Reviewed-on: https://skia-review.googlesource.com/9461
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/tests/ClipStackTest.cpp b/tests/ClipStackTest.cpp
index c2b72c6..31dffcb 100644
--- a/tests/ClipStackTest.cpp
+++ b/tests/ClipStackTest.cpp
@@ -16,6 +16,7 @@
 #include "GrClipStackClip.h"
 #include "GrReducedClip.h"
 #include "GrResourceCache.h"
+#include "GrTextureProxy.h"
 typedef GrReducedClip::ElementList ElementList;
 typedef GrReducedClip::InitialState InitialState;
 #endif