don't adapt any gray colors to 565

Adapting gray to 565 will add a noticeable purple/green tint.
I'd rather only the 565 images in Gold were tainted with that.

Change-Id: Ib09e92b2f78c6de086345124e9eefeb31bbb5fa8
Reviewed-on: https://skia-review.googlesource.com/147422
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/tools/sk_tool_utils.cpp b/tools/sk_tool_utils.cpp
index ae6e90f..9bff574 100644
--- a/tools/sk_tool_utils.cpp
+++ b/tools/sk_tool_utils.cpp
@@ -62,6 +62,12 @@
 }
 
 SkColor color_to_565(SkColor color) {
+    // Not a good idea to use this function for greyscale colors...
+    // it will add an obvious purple or green tint.
+    SkASSERT(SkColorGetR(color) != SkColorGetG(color) ||
+             SkColorGetR(color) != SkColorGetB(color) ||
+             SkColorGetG(color) != SkColorGetB(color));
+
     SkPMColor pmColor = SkPreMultiplyColor(color);
     U16CPU color16 = SkPixel32ToPixel16(pmColor);
     return SkPixel16ToColor(color16);