Broke GrTessellatingPathRenderer's tessellator out into a separate file.

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1557083002

Committed: https://skia.googlesource.com/skia/+/8b05cb8a00bdb82e100f1ba74bf4de4a504cceea

Review URL: https://codereview.chromium.org/1557083002

gyp/gpu.gypi

@@ -161,6 +161,8 @@
       '<(skia_src_path)/gpu/GrStencilAttachment.h',
       '<(skia_src_path)/gpu/GrStrokeInfo.cpp',
       '<(skia_src_path)/gpu/GrStrokeInfo.h',
+      '<(skia_src_path)/gpu/GrTessellator.cpp',
+      '<(skia_src_path)/gpu/GrTessellator.h',
       '<(skia_src_path)/gpu/GrTraceMarker.cpp',
       '<(skia_src_path)/gpu/GrTraceMarker.h',
       '<(skia_src_path)/gpu/GrTracing.h',

src/gpu/GrTessellator.h

@@ -0,0 +1,40 @@
+/*
+ * 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 GrTessellator_DEFINED
+#define GrTessellator_DEFINED
+
+#include "SkPath.h"
+#include "GrResourceProvider.h"
+
+/**
+ * Provides utility functions for converting paths to a collection of triangles.
+ */
+
+#define TESSELLATOR_WIREFRAME 0
+
+namespace GrTessellator {
+
+struct WindingVertex {
+    SkPoint fPos;
+    int fWinding;
+};
+
+// Triangulates a path to an array of vertices. Each triangle is represented as a set of three
+// WindingVertex entries, each of which contains the position and winding count (which is the same
+// for all three vertices of a triangle). The 'verts' out parameter is set to point to the resultant
+// vertex array. CALLER IS RESPONSIBLE for deleting this buffer to avoid a memory leak!
+int PathToVertices(const SkPath& path, SkScalar tolerance, const SkRect& clipBounds, 
+                   WindingVertex** verts);
+
+int PathToTriangles(const SkPath& path, SkScalar tolerance, const SkRect& clipBounds, 
+                    GrResourceProvider* resourceProvider, 
+                    SkAutoTUnref<GrVertexBuffer>& vertexBuffer, bool canMapVB, bool* isLinear);
+
+}
+
+#endif