fix clamp_0/clamp_1 stages in lowp

The existing strategy for skipping them never worked, and the new test
would have crashed.  Instead just make them normal but trivial stages.

Change-Id: I41772e817e52f585b2b90680fdd1781025caf2d1
Reviewed-on: https://skia-review.googlesource.com/148981
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/tests/SkRasterPipelineTest.cpp b/tests/SkRasterPipelineTest.cpp
index 4c76587..ee7816b 100644
--- a/tests/SkRasterPipelineTest.cpp
+++ b/tests/SkRasterPipelineTest.cpp
@@ -185,3 +185,19 @@
         }
     }
 }
+
+DEF_TEST(SkRasterPipeline_lowp_clamp01, r) {
+    // This may seem like a funny pipeline to create,
+    // but it certainly shouldn't crash when you run it.
+
+    uint32_t rgba = 0xff00ff00;
+
+    SkJumper_MemoryCtx ptr = { &rgba, 0 };
+
+    SkRasterPipeline_<256> p;
+    p.append(SkRasterPipeline::load_bgra,  &ptr);
+    p.append(SkRasterPipeline::clamp_0);
+    p.append(SkRasterPipeline::clamp_1);
+    p.append(SkRasterPipeline::store_8888, &ptr);
+    p.run(0,0,1,1);
+}