make tests portable by using 565 compatible colors

TBR=reed@google.com

Review URL: https://codereview.chromium.org/1262703002
diff --git a/gm/mipmap.cpp b/gm/mipmap.cpp
index ad45a17..6163a3a 100644
--- a/gm/mipmap.cpp
+++ b/gm/mipmap.cpp
@@ -15,7 +15,7 @@
     const SkImageInfo info = SkImageInfo::MakeN32Premul(319, 52);
     SkAutoTUnref<SkSurface> surface(SkSurface::NewRaster(info));
     SkCanvas* canvas = surface->getCanvas();
-    canvas->drawColor(0xFFF8F8F8);
+    canvas->drawColor(sk_tool_utils::color_to_565(0xFFF8F8F8));
 
     SkPaint paint;
     paint.setAntiAlias(true);