Add constant color GrFP.

include/gpu/effects/GrConstColorProcessor.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrColorProcessor_DEFINED
+#define GrColorProcessor_DEFINED
+
+#include "GrFragmentProcessor.h"
+
+class GrInvariantOutput;
+
+/**
+ * This is a simple GrFragmentProcessor that outputs a constant color. It may do one of the
+ * following with its input color: ignore it, or multiply it by the constant color, multiply its
+ * alpha by the constant color and ignore the input color's r, g, and b.
+ */
+class GrConstColorProcessor : public GrFragmentProcessor {
+public:
+    enum InputMode {
+        kIgnore_InputMode,
+        kModulateRGBA_InputMode,
+        kModulateA_InputMode,
+
+        kLastInputMode = kModulateA_InputMode
+    };
+    static const int kInputModeCnt = kLastInputMode + 1;
+
+    static GrFragmentProcessor* Create(GrColor color, InputMode mode) {
+        return SkNEW_ARGS(GrConstColorProcessor, (color, mode));
+    }
+
+    ~GrConstColorProcessor() override {}
+
+    const char* name() const override { return "Color"; }
+
+    void getGLProcessorKey(const GrGLCaps&, GrProcessorKeyBuilder*) const override;
+
+    GrGLFragmentProcessor* createGLInstance() const override;
+
+    GrColor color() const { return fColor; }
+
+    InputMode inputMode() const { return fMode; }
+
+private:
+    GrConstColorProcessor(GrColor color, InputMode mode) : fColor(color), fMode(mode) {
+        this->initClassID<GrConstColorProcessor>();
+    }
+
+    bool onIsEqual(const GrFragmentProcessor&) const override;
+
+    void onComputeInvariantOutput(GrInvariantOutput* inout) const override;
+
+    GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
+
+    GrColor     fColor;
+    InputMode   fMode;
+
+    typedef GrFragmentProcessor INHERITED;
+};
+
+#endif