make tests portable by using 565 compatible colors

gm/addarc.cpp

Index: gm/addarc.cpp
diff --git a/gm/addarc.cpp b/gm/addarc.cpp
index 742f16fce5f6d41b67ace89a9f39caba8333b521..3bfed8d549dfccbf3bee485b50a5df7b72f45732 100644
--- a/gm/addarc.cpp
+++ b/gm/addarc.cpp
@@ -36,7 +36,7 @@ protected:
 
         SkScalar sign = 1;
         while (r.width() > paint.getStrokeWidth() * 3) {
-            paint.setColor(rand.nextU() | (0xFF << 24));
+            paint.setColor(sk_tool_utils::color_to_565(rand.nextU() | (0xFF << 24)));
             SkScalar startAngle = rand.nextUScalar1() * 360;
 
             SkScalar speed = SkScalarSqrt(16 / r.width()) * 0.5f;
@@ -144,7 +144,7 @@ protected:
             SkAutoCanvasRestore acr(canvas, true);
             canvas->rotate(fRotate * sign);
 
-            paint.setColor(rand.nextU() | (0xFF << 24));
+            paint.setColor(sk_tool_utils::color_to_565(rand.nextU() | (0xFF << 24)));
             canvas->drawOval(r, paint);
             r.inset(delta, delta);
             sign = -sign;