Add iOS to platform_os_emoji.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2164783004

Review-Url: https://codereview.chromium.org/2164783004
diff --git a/tools/sk_tool_utils.cpp b/tools/sk_tool_utils.cpp
index 8303f09..9f398e2 100644
--- a/tools/sk_tool_utils.cpp
+++ b/tools/sk_tool_utils.cpp
@@ -71,7 +71,7 @@
     if (!strcmp(osName, "Android") || !strcmp(osName, "Ubuntu")) {
         return "CBDT";
     }
-    if (!strncmp(osName, "Mac", 3)) {
+    if (!strncmp(osName, "Mac", 3) || !strncmp(osName, "iOS", 3)) {
         return "SBIX";
     }
     if (!strncmp(osName, "Win", 3)) {