Add helper for creating leaf FPs inside GrFP::TestCreate functions

src/gpu/GrProcessorUnitTest.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "GrProcessorUnitTest.h"
+#include "GrFragmentProcessor.h"
+
+const GrFragmentProcessor* GrProcessorUnitTest::CreateChildFP(GrProcessorTestData* data) {
+#if SK_ALLOW_STATIC_GLOBAL_INITIALIZERS
+    SkAutoTUnref<const GrFragmentProcessor> fp;
+    do {
+        fp.reset(GrProcessorTestFactory<GrFragmentProcessor>::Create(data));
+        SkASSERT(fp);
+    } while (fp->numChildProcessors() != 0);
+    return SkRef(fp.get());
+#else
+    SkFAIL("Should not be called if !SK_ALLOW_STATIC_GLOBAL_INITIALIZERS");
+    return nullptr;
+#endif
+}