Turn on MPD threading in nanobench.

src/core/SkBitmapProcShader.cpp

Index: src/core/SkBitmapProcShader.cpp
diff --git a/src/core/SkBitmapProcShader.cpp b/src/core/SkBitmapProcShader.cpp
index f01d55905824a34b3bfaa154fcaf0fb68c623abd..2e42ef1b9a2e3e76d41ee59982600d92b2ccbdd4 100644
--- a/src/core/SkBitmapProcShader.cpp
+++ b/src/core/SkBitmapProcShader.cpp
@@ -92,9 +92,9 @@ static bool valid_for_drawing(const SkBitmap& bm) {
         return false;   // no pixels to read
     }
     if (kIndex_8_SkColorType == bm.colorType()) {
-        // ugh, I have to lock-pixels to inspect the colortable
-        SkAutoLockPixels alp(bm);
-        if (!bm.getColorTable()) {
+        SkBitmap copy(bm);          // Locking and unlocking pixels is not thread safe,
+        SkAutoLockPixels alp(copy); // but we need to call it before getColorTable() is safe.
+        if (!copy.getColorTable()) {
             return false;
         }
     }