Revert of Revert of make gm background colors 565 compatible

tools/sk_tool_utils.cpp

Index: tools/sk_tool_utils.cpp
diff --git a/tools/sk_tool_utils.cpp b/tools/sk_tool_utils.cpp
index ec7942b165e7a77026c827320df3fc8c3ae16000..4d0e0bde68fffcb756454a4a1bb89b044c7e859c 100644
--- a/tools/sk_tool_utils.cpp
+++ b/tools/sk_tool_utils.cpp
@@ -34,10 +34,10 @@
     }
 }
 
-void color_to_565(SkColor* color) {
-    SkPMColor pmColor = SkPreMultiplyColor(*color);
+SkColor color_to_565(SkColor color) {
+    SkPMColor pmColor = SkPreMultiplyColor(color);
     U16CPU color16 = SkPixel32ToPixel16(pmColor);
-    *color = SkPixel16ToColor(color16);
+    return SkPixel16ToColor(color16);
 }
 
 SkTypeface* create_portable_typeface(const char* name, SkTypeface::Style style) {