update cliptype test to exercise clipstack backend

BUG=skia:

Change-Id: Iaa54dd8d556db3cead723558e812d927376b08c0
Reviewed-on: https://skia-review.googlesource.com/9186
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/tests/CanvasTest.cpp b/tests/CanvasTest.cpp
index af18938..e84b7ba 100644
--- a/tests/CanvasTest.cpp
+++ b/tests/CanvasTest.cpp
@@ -814,10 +814,7 @@
     REPORTER_ASSERT(r, !life[1]);
 }
 
-DEF_TEST(CanvasClipType, r) {
-    sk_sp<SkSurface> surf = SkSurface::MakeRasterN32Premul(10, 10);
-    SkCanvas* canvas = surf->getCanvas();
-
+static void test_cliptype(SkCanvas* canvas, skiatest::Reporter* r) {
     REPORTER_ASSERT(r, !canvas->isClipEmpty());
     REPORTER_ASSERT(r, canvas->isClipRect());
 
@@ -842,3 +839,12 @@
     REPORTER_ASSERT(r, !canvas->isClipEmpty());
     REPORTER_ASSERT(r, canvas->isClipRect());
 }
+
+DEF_TEST(CanvasClipType, r) {
+    // test rasterclip backend
+    test_cliptype(SkSurface::MakeRasterN32Premul(10, 10)->getCanvas(), r);
+
+    // test clipstack backend
+    SkDynamicMemoryWStream stream;
+    test_cliptype(SkDocument::MakePDF(&stream)->beginPage(100, 100), r);
+}