Test that GrFragmentProcessors work without input colors.

include/gpu/GrProcessorUnitTest.h

Index: include/gpu/GrProcessorUnitTest.h
diff --git a/include/gpu/GrProcessorUnitTest.h b/include/gpu/GrProcessorUnitTest.h
index 66ba2396029724925e1214c0f4729b23098e3855..8a17521bfce2bfd6f92f77c992301759de70285f 100644
--- a/include/gpu/GrProcessorUnitTest.h
+++ b/include/gpu/GrProcessorUnitTest.h
@@ -68,10 +68,19 @@ public:
         GetFactories()->push_back(this);
     }
 
-    static const Processor* CreateStage(GrProcessorTestData* data) {
+    /** Pick a random factory function and create a processor.  */
+    static const Processor* Create(GrProcessorTestData* data) {
         VerifyFactoryCount();
         SkASSERT(GetFactories()->count());
         uint32_t idx = data->fRandom->nextRangeU(0, GetFactories()->count() - 1);
+        return CreateIdx(idx, data);
+    }
+
+    /** Number of registered factory functions */
+    static int Count() { return GetFactories()->count(); }
+
+    /** Use factory function at Index idx to create a processor. */
+    static const Processor* CreateIdx(int idx, GrProcessorTestData* data) {
         GrProcessorTestFactory<Processor>* factory = (*GetFactories())[idx];
         return factory->fCreateProc(data);
     }