Add constant for blitter context size.

bench/SkLinearBitmapPipelineBench.cpp

Index: bench/SkLinearBitmapPipelineBench.cpp
diff --git a/bench/SkLinearBitmapPipelineBench.cpp b/bench/SkLinearBitmapPipelineBench.cpp
index f111aeea9ea1180bac515b4ad2150695a0fdcb0c..caf1844f59389c1d8355bb6e481b3bef1c9deacc 100644
--- a/bench/SkLinearBitmapPipelineBench.cpp
+++ b/bench/SkLinearBitmapPipelineBench.cpp
@@ -8,6 +8,7 @@
 #include <memory>
 #include "SkColor.h"
 #include "SkLinearBitmapPipeline.h"
+#include "SkBitmapProcShader.h"
 #include "SkPM4f.h"
 #include "Benchmark.h"
 #include "SkShader.h"
@@ -193,7 +194,7 @@ struct SkBitmapFPOrigShader : public CommonBitmapFPBenchmark {
 
         SkAutoTMalloc<SkPMColor> buffer4b(width*height);
 
-        uint32_t storage[300];
+        uint32_t storage[kSkBlitterContextSize];
         const SkShader::ContextRec rec(fPaint, fM, nullptr,
                                        SkShader::ContextRec::kPMColor_DstType);
         SkASSERT(fPaint.getShader()->contextSize(rec) <= sizeof(storage));