skrpb: evaluate color filters for constant shaders once.

src/core/SkRasterPipeline.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 SkRasterPipeline_DEFINED
 #define SkRasterPipeline_DEFINED
 
@@ skipping 38 matching lines @@
  *
  * Some stages that typically return are those that write a color to a destination pointer,
  * but any stage can short-circuit the rest of the pipeline by returning instead of calling next().
  */
 
 // TODO: There may be a better place to stuff tail, e.g. in the bottom alignment bits of
 // the Stage*.  This mostly matters on 64-bit Windows where every register is precious.
 
 #define SK_RASTER_PIPELINE_STAGES(M)                             \
     M(swap_src_dst) M(clamp_0) M(clamp_a) M(unpremul) M(premul)  \
-    M(constant_color)                                            \
+    M(constant_color) M(store_f32)                               \
     M(load_s_565)  M(load_d_565)  M(store_565)                   \
     M(load_s_srgb) M(load_d_srgb) M(store_srgb)                  \
     M(load_s_f16)  M(load_d_f16)  M(store_f16)                   \
     M(scale_u8) M(scale_constant_float)                          \
     M(lerp_u8) M(lerp_565) M(lerp_constant_float)                \
     M(dst)                                                       \
     M(dstatop) M(dstin) M(dstout) M(dstover)                     \
     M(srcatop) M(srcin) M(srcout) M(srcover)                     \
     M(clear) M(modulate) M(multiply) M(plus_) M(screen) M(xor_)  \
     M(colorburn) M(colordodge) M(darken) M(difference)           \
@@ skipping 25 matching lines @@
         StockStage stage;
         void*        ctx;
     };
 
 private:
     int   fNum   = 0;
     Stage fStages[kMaxStages];
 };
 
 #endif//SkRasterPipeline_DEFINED