Transparent apps support

chrome/common/extensions/api/app_window.idl

Index: chrome/common/extensions/api/app_window.idl
diff --git a/chrome/common/extensions/api/app_window.idl b/chrome/common/extensions/api/app_window.idl
index 1d3953d1a4417f623aed6c470e4172d2ecd5ebca..5bc317f7c497114c4abe52e045ded8fdd502be43 100644
--- a/chrome/common/extensions/api/app_window.idl
+++ b/chrome/common/extensions/api/app_window.idl
@@ -49,7 +49,7 @@ namespace app.window {
     // Maximum height of the window.
     long? maxHeight;
 
-    // Window type: 
+    // Window type:
     //  'shell' - the default window type
     //  'panel' - a panel, managed by the OS (Currently experimental, Ash only)
     [nodoc] DOMString? type;
@@ -63,6 +63,10 @@ namespace app.window {
     // precedence.
     Bounds? bounds;
 
+    // Enable window background transparency.
+    // Only supported in ash. Requires experimental API permission.
+    boolean? transparentBackground;
+
     // If true, the window will be created in a hidden state. Call show() on
     // the window to show it once it has been created. Defaults to false.
     boolean? hidden;