Add support for transparent background API

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 0b2d3e85d2bef7adfc34e5ed8d8641e73f282659..f52491029b5a4f03c1b94ecf9ab7f0f6ad92c3d0 100644
--- a/chrome/common/extensions/api/app_window.idl
+++ b/chrome/common/extensions/api/app_window.idl
@@ -221,8 +221,8 @@ namespace app.window {
     [deprecated="Use innerBounds or outerBounds."] ContentBounds? bounds;
 
     // Enable window background transparency.
-    // Only supported in ash. Requires experimental API permission.
-    boolean? transparentBackground;
+    // Only supported in ash. Requires app.window.alpha API permission.
+    boolean? alphaEnabled;
 
     // The initial state of the window, allowing it to be created already
     // fullscreen, maximized, or minimized. Defaults to 'normal'.
@@ -349,6 +349,9 @@ namespace app.window {
     // <code>"app.window.alwaysOnTop"</code> permission.
     static void setAlwaysOnTop(boolean alwaysOnTop);
 
+    // Does the window allow a transparent background?
+    static boolean alphaEnabled();
+
     // The JavaScript 'window' object for the created child.
     [instanceOf=Window] object contentWindow;
 
@@ -418,6 +421,9 @@ namespace app.window {
     // Fired when the window is fullscreened.
     [nocompile] static void onFullscreened();
 
+    // Fired when the alphaEnabled flag changes.
+    [nocompile] static void onAlphaEnabledChanged();
+
     // Fired when the window is maximized.
     [nocompile] static void onMaximized();