Add app.window.alphaEnabled() and onAlphaEnabledChanged.

chrome/browser/extensions/api/app_window/app_window_api.cc

Index: chrome/browser/extensions/api/app_window/app_window_api.cc
diff --git a/chrome/browser/extensions/api/app_window/app_window_api.cc b/chrome/browser/extensions/api/app_window/app_window_api.cc
index 199fbf4b9afcf5c70f65f9c120e15ee1d71df112..4c117501ad1bd2fcef519046d740e86469d1a833 100644
--- a/chrome/browser/extensions/api/app_window/app_window_api.cc
+++ b/chrome/browser/extensions/api/app_window/app_window_api.cc
@@ -54,6 +54,8 @@ const char kAlwaysOnTopPermission[] =
     "The \"app.window.alwaysOnTop\" permission is required.";
 const char kInvalidUrlParameter[] =
     "The URL used for window creation must be local for security reasons.";
+const char kTransparentBackgroundNeedsFrameNone[] =
+    "\"transparent_background\" can only be used with \"frame: none\".";
 }  // namespace app_window_constants
 
 const char kNoneFrameOption[] = "none";
@@ -232,12 +234,17 @@ bool AppWindowCreateFunction::RunAsync() {
     if (!GetFrameOptions(*options, &create_params))
       return false;
 
-    if (options->transparent_background.get() &&
-        (GetExtension()->permissions_data()->HasAPIPermission(
-             APIPermission::kExperimental) ||
-         CommandLine::ForCurrentProcess()->HasSwitch(
-             switches::kEnableExperimentalExtensionApis))) {
-      create_params.transparent_background = *options->transparent_background;
+    if (options->transparent_background.get()) {

[Wez, 2014/07/11 17:14:10]

Not necessarily for this CL:

Can we re-name this option to alpha_background or similar, and have the JS API
accept backgroundAlpha or transparentBackground options (so we don't break our
existing test app :)?

[jackhou1, 2014/07/14 03:08:12]

benwells, what do you think of this?
Maybe it should be implemented in the other CL
(https://codereview.chromium.org/190533006/).

+      if (create_params.frame != AppWindow::FRAME_NONE) {
+        error_ = app_window_constants::kTransparentBackgroundNeedsFrameNone;
+        return false;
+      }
+      if (GetExtension()->permissions_data()->HasAPIPermission(
+              APIPermission::kExperimental) ||
+          CommandLine::ForCurrentProcess()->HasSwitch(
+              switches::kEnableExperimentalExtensionApis)) {
+        create_params.transparent_background = *options->transparent_background;
+      }
     }
 
     if (options->hidden.get())