Add clone to Stage. Rename place to mix and PolymorphicUnion to Stage. Cleanup.

tests/SkColor4fTest.cpp

Index: tests/SkColor4fTest.cpp
diff --git a/tests/SkColor4fTest.cpp b/tests/SkColor4fTest.cpp
index 239004aacb35fed695eba2841f247a397244ea44..67e8d37d245cce390beb33957b0b0753eefc500f 100644
--- a/tests/SkColor4fTest.cpp
+++ b/tests/SkColor4fTest.cpp
@@ -153,7 +153,7 @@ DEF_TEST(Color4f_shader, reporter) {
 
     SkPaint paint;
     for (const auto& rec : recs) {
-        uint32_t storage[300];
+        uint32_t storage[400];
         paint.setShader(rec.fFact());
         // Encourage 4f context selection. At some point we may need
         // to instantiate two separate contexts for optimal 4b/4f selection.