Fix X11DesktopHandler::ActivateWindow on Unity for known user gestures

ui/views/widget/desktop_aura/x11_desktop_handler.cc

Index: ui/views/widget/desktop_aura/x11_desktop_handler.cc
diff --git a/ui/views/widget/desktop_aura/x11_desktop_handler.cc b/ui/views/widget/desktop_aura/x11_desktop_handler.cc
index 33b6347958efd04a654db25e6edc6ef636047394..b772d24b3b604c01cfdc79ffc28ce1a2c97a4c54 100644
--- a/ui/views/widget/desktop_aura/x11_desktop_handler.cc
+++ b/ui/views/widget/desktop_aura/x11_desktop_handler.cc
@@ -74,7 +74,8 @@ X11DesktopHandler::~X11DesktopHandler() {
     ui::PlatformEventSource::GetInstance()->RemovePlatformEventDispatcher(this);
 }
 
-void X11DesktopHandler::ActivateWindow(::Window window) {
+void X11DesktopHandler::ActivateWindow(::Window window,
+                                       bool for_user_gesture) {
   if ((current_window_ == None || current_window_ == window) &&
       current_window_active_state_ == NOT_ACTIVE) {
     // |window| is most likely still active wrt to the X server. Undo the
@@ -91,13 +92,29 @@ void X11DesktopHandler::ActivateWindow(::Window window) {
   if (wm_supports_active_window_) {
     DCHECK_EQ(gfx::GetXDisplay(), xdisplay_);
 
+    // According to
+    // http://standards.freedesktop.org/wm-spec/wm-spec-latest.html#sourceindication
+    // "Some requests from Clients include type of the Client, for example the
+    // _NET_ACTIVE_WINDOW message. Currently the types can be 1 for normal
+    // applications, and 2 for pagers and other Clients that represent direct
+    // user actions (the Window Manager may decide to treat requests from
+    // applications differently than requests that are result of direct user
+    // actions)."
+    //
+    // Normally we set the source indication to 1 (normal application), but when
+    // we know activation is being triggered from a user gesture, then we set it
+    // to 2 so the WM properly prioritizes our request. Without this, Unity on
+    // Ubuntu 14.04 ignores requests to activate a window unless some other
+    // Chrome window is already the active window (see issues 470830 & 411702).
+    long source_indication = for_user_gesture ? 2 : 1;
+
     XEvent xclient;
     memset(&xclient, 0, sizeof(xclient));
     xclient.type = ClientMessage;
     xclient.xclient.window = window;
     xclient.xclient.message_type = atom_cache_.GetAtom("_NET_ACTIVE_WINDOW");
     xclient.xclient.format = 32;
-    xclient.xclient.data.l[0] = 1;  // Specified we are an app.
+    xclient.xclient.data.l[0] = source_indication;
     xclient.xclient.data.l[1] = wm_user_time_ms_;
     xclient.xclient.data.l[2] = None;
     xclient.xclient.data.l[3] = 0;