[Emoji] Enable by default on the Mac platform.

Bug: 827404
Change-Id: I30e9c4d44aa3c6583fbe26743dab964e99011d28
Reviewed-on: https://chromium-review.googlesource.com/1101642Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567444}

ui/base/ui_base_features.cc

@@ -14,8 +14,14 @@ namespace features {
 
 // If enabled, the emoji picker context menu item may be shown for editable
 // text areas.
-const base::Feature kEnableEmojiContextMenu{"EnableEmojiContextMenu",
-                                            base::FEATURE_DISABLED_BY_DEFAULT};
+const base::Feature kEnableEmojiContextMenu {
+  "EnableEmojiContextMenu",
+#if defined(OS_MACOSX)
+      base::FEATURE_ENABLED_BY_DEFAULT
+#else
+      base::FEATURE_DISABLED_BY_DEFAULT
+#endif
+};
 
 // Enables the floating virtual keyboard behavior.
 const base::Feature kEnableFloatingVirtualKeyboard = {