SkRasterPipeline: simplify impl and remove need to rewire stages

tests/SkRasterPipelineTest.cpp

Index: tests/SkRasterPipelineTest.cpp
diff --git a/tests/SkRasterPipelineTest.cpp b/tests/SkRasterPipelineTest.cpp
index 1db020670505a67e38980c0e29aef0712eafb14f..beb517b3f7aca5cc7c45dd86eaab1e2aef530093 100644
--- a/tests/SkRasterPipelineTest.cpp
+++ b/tests/SkRasterPipelineTest.cpp
@@ -85,3 +85,17 @@ DEF_TEST(SkRasterPipeline, r) {
     REPORTER_ASSERT(r, dst_vals[3] == 16);
     REPORTER_ASSERT(r, dst_vals[4] == 25);
 }
+
+DEF_TEST(SkRasterPipeline_empty, r) {
+    // No asserts... just a test that this is safe to run.
+    SkRasterPipeline p;
+    p.run(20);
+}
+
+DEF_TEST(SkRasterPipeline_nonsense, r) {
+    // No asserts... just a test that this is safe to run and terminates.
+    // square() always calls st->next(); this makes sure we've always got something there to call.
+    SkRasterPipeline p;
+    p.append(square);
+    p.run(20);
+}