Add constant for blitter context size.

tests/SkColor4fTest.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
+#include "SkBitmapProcShader.h"
 #include "SkColor.h"
 #include "SkColorMatrixFilter.h"
 #include "SkGradientShader.h"
 #include "SkImage.h"
 #include "SkPM4f.h"
 #include "SkShader.h"
 
 #include "Test.h"
 #include "SkRandom.h"
 
@@ skipping 128 matching lines @@
         { make_color_sh, true,  1.0f/255   },
         // PMColor 4f gradients are interpolated in 255-multiplied values, so we need a
         // slightly relaxed tolerance to accommodate the cumulative precision deviation.
         { make_grad_sh,  true,  1.001f/255 },
         { make_image_sh, false, 1.0f/255   },
         { make_cf_sh,    true,  1.0f/255   },
     };
 
     SkPaint paint;
     for (const auto& rec : recs) {
-        uint32_t storage[400];
+        uint32_t storage[kSkBlitterContextSize];
         paint.setShader(rec.fFact());
         // Encourage 4f context selection. At some point we may need
         // to instantiate two separate contexts for optimal 4b/4f selection.
         const SkShader::ContextRec contextRec(paint, SkMatrix::I(), nullptr,
                                               SkShader::ContextRec::kPM4f_DstType);
         SkASSERT(paint.getShader()->contextSize(contextRec) <= sizeof(storage));
         SkShader::Context* ctx = paint.getShader()->createContext(contextRec, storage);
         if (rec.fSupports4f) {
             const int N = 100;
             SkPM4f buffer4f[N];
@@ skipping 73 matching lines @@
 //
 DEF_TEST(Color4f_xfermode_proc4f, reporter) {
     // TODO: extend xfermodes so that all cases can be tested.
     //
     for (int mode = SkXfermode::kClear_Mode; mode <= SkXfermode::kScreen_Mode; ++mode) {
         SkXfermodeProc   proc32 = SkXfermode::GetProc((SkXfermode::Mode)mode);
         SkXfermodeProc4f proc4f = SkXfermode::GetProc4f((SkXfermode::Mode)mode);
         REPORTER_ASSERT(reporter, compare_procs(proc32, proc4f));
     }
 }