Make onPrepareDraws const

src/gpu/GrPathUtils.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrPathUtils_DEFINED
 #define GrPathUtils_DEFINED
 
@@ skipping 56 matching lines @@
          * and reorder to avoid stalling for loads. The assumption is that a
          * path renderer will have a small fixed number of vertices that it
          * uploads for each quad.
          *
          * N is the number of vertices.
          * STRIDE is the size of each vertex.
          * UV_OFFSET is the offset of the UV values within each vertex.
          * vertices is a pointer to the first vertex.
          */
         template <int N, size_t STRIDE, size_t UV_OFFSET>
-        void apply(const void* vertices) {
+        void apply(const void* vertices) const {
             intptr_t xyPtr = reinterpret_cast<intptr_t>(vertices);
             intptr_t uvPtr = reinterpret_cast<intptr_t>(vertices) + UV_OFFSET;
             float sx = fM[0];
             float kx = fM[1];
             float tx = fM[2];
             float ky = fM[3];
             float sy = fM[4];
             float ty = fM[5];
             for (int i = 0; i < N; ++i) {
                 const SkPoint* xy = reinterpret_cast<const SkPoint*>(xyPtr);
@@ skipping 82 matching lines @@
     void getCubicKLM(const SkPoint p[4], SkScalar klm[9]);
 
     // When tessellating curved paths into linear segments, this defines the maximum distance
     // in screen space which a segment may deviate from the mathmatically correct value.
     // Above this value, the segment will be subdivided.
     // This value was chosen to approximate the supersampling accuracy of the raster path (16
     // samples, or one quarter pixel).
     static const SkScalar kDefaultTolerance = SkDoubleToScalar(0.25);
 };
 #endif