Add XP to handle the cases where we disable color write.

src/gpu/effects/GrDisableColorXP.h

Index: src/gpu/effects/GrDisableColorXP.h
diff --git a/src/gpu/effects/GrDisableColorXP.h b/src/gpu/effects/GrDisableColorXP.h
new file mode 100644
index 0000000000000000000000000000000000000000..b0de66bf438b14c447a81a445f072421afb4322a
--- /dev/null
+++ b/src/gpu/effects/GrDisableColorXP.h
@@ -0,0 +1,102 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrDisableColorXP_DEFINED
+#define GrDisableColorXP_DEFINED
+
+#include "GrTypes.h"
+#include "GrXferProcessor.h"
+
+class GrProcOptInfo;
+
+/**
+ * This xfer processor disables color writing. Thus color and coverage and ignored and no blending
+ * occurs. This XP is usful for things like stenciling.
+ */
+class GrDisableColorXP : public GrXferProcessor {
+public:
+    static GrXferProcessor* Create() {
+        return SkNEW(GrDisableColorXP);
+    }
+
+    ~GrDisableColorXP() SK_OVERRIDE {};
+
+    const char* name() const SK_OVERRIDE { return "Disable Color"; }
+
+    void getGLProcessorKey(const GrGLCaps& caps, GrProcessorKeyBuilder* b) const SK_OVERRIDE;
+
+    GrGLXferProcessor* createGLInstance() const SK_OVERRIDE;
+
+    bool hasSecondaryOutput() const SK_OVERRIDE { return false; }
+
+    GrXferProcessor::OptFlags getOptimizations(const GrProcOptInfo& colorPOI,
+                                               const GrProcOptInfo& coveragePOI,
+                                               bool doesStencilWrite,
+                                               GrColor* color,
+                                               const GrDrawTargetCaps& caps) SK_OVERRIDE {
+        return GrXferProcessor::kIgnoreColor_OptFlag | GrXferProcessor::kIgnoreCoverage_OptFlag;
+    }
+
+    void getBlendInfo(GrXferProcessor::BlendInfo* blendInfo) const SK_OVERRIDE;
+
+private:
+    GrDisableColorXP();
+
+    bool onIsEqual(const GrXferProcessor& xpBase) const SK_OVERRIDE {
+        return true;
+    }
+
+    typedef GrXferProcessor INHERITED;
+};
+
+///////////////////////////////////////////////////////////////////////////////
+
+class GrDisableColorXPFactory : public GrXPFactory {
+public:
+    static GrXPFactory* Create() {
+        return SkNEW(GrDisableColorXPFactory);
+    }
+
+    GrXferProcessor* createXferProcessor(const GrProcOptInfo& colorPOI,
+                                         const GrProcOptInfo& coveragePOI) const SK_OVERRIDE;
+
+    bool supportsRGBCoverage(GrColor knownColor, uint32_t knownColorFlags) const SK_OVERRIDE {
+        return true;
+    }
+
+    bool canApplyCoverage(const GrProcOptInfo& colorPOI,
+                          const GrProcOptInfo& coveragePOI) const SK_OVERRIDE {
+        return true;
+    }
+
+    bool canTweakAlphaForCoverage() const SK_OVERRIDE { return true; }
+
+    void getInvariantOutput(const GrProcOptInfo& colorPOI, const GrProcOptInfo& coveragePOI,
+                            GrXPFactory::InvariantOutput* output) const SK_OVERRIDE {
+        output->fBlendedColorFlags = 0;
+        output->fWillBlendWithDst = 0;
+    }
+
+    bool willReadDst(const GrProcOptInfo& colorPOI,
+                     const GrProcOptInfo& coveragePOI) const SK_OVERRIDE {
+        return false;
+    }
+
+private:
+    GrDisableColorXPFactory();
+
+    bool onIsEqual(const GrXPFactory& xpfBase) const SK_OVERRIDE {
+        return true;
+    }
+
+    GR_DECLARE_XP_FACTORY_TEST;
+
+    typedef GrXPFactory INHERITED;
+};
+
+#endif
+