Add explicit double -> SkScalar conversion to fix werror on Windows.

bench/RectBench.cpp

Index: bench/RectBench.cpp
diff --git a/bench/RectBench.cpp b/bench/RectBench.cpp
index ebf270d8e346e84ac7ec8b13350f2f520808ab58..22c26456e3b264b4e99bc361924507e5a3370408 100644
--- a/bench/RectBench.cpp
+++ b/bench/RectBench.cpp
@@ -148,7 +148,7 @@ protected:
         size_t sizes = SK_ARRAY_COUNT(gSizes);
 
         if (FLAGS_strokeWidth >= 0) {
-            gSizes[0] = FLAGS_strokeWidth;
+            gSizes[0] = (SkScalar)FLAGS_strokeWidth;
             sizes = 1;
         }
 
@@ -250,7 +250,7 @@ protected:
         size_t sizes = SK_ARRAY_COUNT(gSizes);
 
         if (FLAGS_strokeWidth >= 0) {
-            gSizes[0] = FLAGS_strokeWidth;
+            gSizes[0] = (SkScalar)FLAGS_strokeWidth;
             sizes = 1;
         }
         SkRandom rand;