Split AlphaThresholdEffect out into its own file

src/effects/GrAlphaThresholdFragmentProcessor.h

Index: src/effects/GrAlphaThresholdFragmentProcessor.h
diff --git a/src/effects/GrAlphaThresholdFragmentProcessor.h b/src/effects/GrAlphaThresholdFragmentProcessor.h
new file mode 100644
index 0000000000000000000000000000000000000000..be04e22b444ba30da134f4b04cdc9352332df70a
--- /dev/null
+++ b/src/effects/GrAlphaThresholdFragmentProcessor.h
@@ -0,0 +1,61 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrAlphaThresholdFragmentProcessor_DEFINED
+#define GrAlphaThresholdFragmentProcessor_DEFINED
+
+#include "SkTypes.h"
+
+#if SK_SUPPORT_GPU
+
+#include "GrCoordTransform.h"
+#include "GrFragmentProcessor.h"
+#include "GrProcessorUnitTest.h"
+
+class GrAlphaThresholdFragmentProcessor : public GrFragmentProcessor {
+
+public:
+    static sk_sp<GrFragmentProcessor> Make(GrTexture* texture,
+                                           GrTexture* maskTexture,
+                                           float innerThreshold,
+                                           float outerThreshold,
+                                           const SkIRect& bounds);
+
+    const char* name() const override { return "Alpha Threshold"; }
+
+    float innerThreshold() const { return fInnerThreshold; }
+    float outerThreshold() const { return fOuterThreshold; }
+
+private:
+    GrAlphaThresholdFragmentProcessor(GrTexture* texture,
+                                      GrTexture* maskTexture,
+                                      float innerThreshold,
+                                      float outerThreshold,
+                                      const SkIRect& bounds);
+
+    GrGLSLFragmentProcessor* onCreateGLSLInstance() const override;
+
+    void onGetGLSLProcessorKey(const GrGLSLCaps&, GrProcessorKeyBuilder*) const override;
+
+    bool onIsEqual(const GrFragmentProcessor&) const override;
+
+    void onComputeInvariantOutput(GrInvariantOutput* inout) const override;
+
+    GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
+
+    float fInnerThreshold;
+    float fOuterThreshold;
+    GrCoordTransform fImageCoordTransform;
+    GrTextureAccess  fImageTextureAccess;
+    GrCoordTransform fMaskCoordTransform;
+    GrTextureAccess  fMaskTextureAccess;
+
+    typedef GrFragmentProcessor INHERITED;
+};
+
+#endif
+#endif