Reduce stack usage for tests.

TBR=mtklein@google.com

Change-Id: Id7621548995b368164d74c817e288c34ef656bfb
Reviewed-on: https://skia-review.googlesource.com/8180
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Herb Derby <herb@google.com>
diff --git a/bench/SkLinearBitmapPipelineBench.cpp b/bench/SkLinearBitmapPipelineBench.cpp
index 29f2889..8391a0f 100644
--- a/bench/SkLinearBitmapPipelineBench.cpp
+++ b/bench/SkLinearBitmapPipelineBench.cpp
@@ -201,7 +201,7 @@
 
         SkAutoTMalloc<SkPMColor> buffer4b(width*height);
 
-        SkArenaAlloc alloc{kSkBlitterContextSize * sizeof(uint32_t)};
+        SkArenaAlloc alloc{0};
         const SkShader::ContextRec rec(fPaint, fM, nullptr,
                                        SkShader::ContextRec::kPMColor_DstType,
                                        nullptr);