Set analytic AA as default.

src/core/SkSRGB.h

 /*
  * 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 SkSRGB_DEFINED
 #define SkSRGB_DEFINED
 
@@ skipping 43 matching lines @@
 template <int N>
 static inline SkNx<N,int> sk_linear_to_srgb(const SkNx<N,float>& x) {
     auto f = sk_linear_to_srgb_needs_trunc(x);
     return SkNx_cast<int>(sk_clamp_0_255(f));
 }
 
 template <int N>
 static inline SkNx<N,int> sk_linear_to_srgb_noclamp(const SkNx<N,float>& x) {
     auto f = sk_linear_to_srgb_needs_trunc(x);
     for (int i = 0; i < 4; i++) {
-        SkASSERTF(0.0f <= f[i] && f[i] < 256.0f, "f[%d] was %g, outside [0,256)\n", i, f[i]);
+        // Turn this assert off for now because srgb conversions may end up in rgb > a
+        // SkASSERTF(0.0f <= f[i] && f[i] < 256.0f, "f[%d] was %g, outside [0,256)\n", i, f[i]);

[mtklein_C, 2016/11/02 18:48:19]

There's a slightly better solution, which is to delete this function completely,
and edit SkRasterPipeline_opts.h to call sk_linear_to_srgb() instead of
sk_linear_to_srgb_noclamp().

If you don't want to complicate this CL with that, that's fine.  I can land that
change first or as a follow up.

[liyuqian, 2016/11/02 19:33:11]

Thank you! I saw your follow up CL. Feel free to land it first as I'm still
debugging the serialize tests issue.

     }
     return SkNx_cast<int>(f);
 }
 
 // sRGB -> linear, using math instead of table lookups, scaling better to larger SIMD vectors.
 template <int N>
 static inline SkNx<N,float> sk_linear_from_srgb_math(const SkNx<N,int>& s) {
     auto x = SkNx_cast<float>(s);
 
     const float u = 1/255.0f;  // x is [0,255], so x^n needs scaling by u^n.
 
     // Non-linear segment of sRGB curve approximated by
     // l = 0.0025 + 0.6975x^2 + 0.3x^3
     const SkNx<N,float> k0 = 0.0025f,
                         k2 = 0.6975f * u*u,
                         k3 = 0.3000f * u*u*u;
     auto hi = SkNx_fma(x*x, SkNx_fma(x, k3, k2), k0);
 
     // Linear segment of sRGB curve: the normal slope, extended a little further than normal.
     auto lo = x * (u/12.92f);
 
     return (x < 14.025f).thenElse(lo, hi);
 }
 
 #endif//SkSRGB_DEFINED