Enhance chrome.app.window API with window background color

extensions/common/api/app_window.idl

Index: extensions/common/api/app_window.idl
diff --git a/extensions/common/api/app_window.idl b/extensions/common/api/app_window.idl
index 999b99990ac882fb04adbe70b37365314a1c761b..d3944395cfdaa790cd077ab0562b64fe3b5de803 100644
--- a/extensions/common/api/app_window.idl
+++ b/extensions/common/api/app_window.idl
@@ -255,6 +255,9 @@ namespace app.window {
     // permission.
     [nodoc] boolean? alphaEnabled;
 
+    // Set window background color.

[Reilly Grant (use Gerrit), 2017/03/10 18:39:18]

Please be more specific about when this parameter is used and the format the
color must be specified in.

+    [nodoc] DOMString? backgroundColor;
+
     // The initial state of the window, allowing it to be created already
     // fullscreen, maximized, or minimized. Defaults to 'normal'.
     State? state;