Disable Panels on OSes other than ChromeOS, in preparation to removing the code.

chrome/browser/ui/panels/panel_manager.cc

Index: chrome/browser/ui/panels/panel_manager.cc
diff --git a/chrome/browser/ui/panels/panel_manager.cc b/chrome/browser/ui/panels/panel_manager.cc
index 7d2c9cec5a78d650b69545e879eab81a9327f98c..3ae9d5c8287c2751cc54f5ae65038b1e88bd9066 100644
--- a/chrome/browser/ui/panels/panel_manager.cc
+++ b/chrome/browser/ui/panels/panel_manager.cc
@@ -131,11 +131,16 @@ bool PanelManager::ShouldUsePanels(const std::string& extension_id) {
   }
 #endif  // USE_X11 && !OS_CHROMEOS
 
-  // Without --enable-panels, only support Hangouts.
+// Panels are an Eraser target. See http://crbug.com/571511 for details.
+// TODO(dimich): remove the rest of Panels code (except ChromeOS) once
+// erasure is stable.
+#if defined(OS_CHROMEOS)
+  // Without --enable-panels, only support Hangouts on ChromeOS.

[stevenjb, 2016/06/22 17:08:33]

This comment is a bit misleading - Chrome OS does not use this code at all.
Maybe we should refer to this feature as "Non Chrome OS Desktop panels" or
something equally awkward? :)

[Dmitry Titov, 2016/06/22 17:53:58]

It is in fact correct, although I agree not very clear. ChromeOS path in
chrome.windows.create is still using static PanelManager::ShouldUsePanels() to
activate. The effect of the change is that this hack will continue to work on
ChromeOS but not on other desktop OSes. Once the disable is stable and Hangouts
team have time to react, I'm planning to clean the code up leaving only ChromeOS
parts, and removing chrome.windows.create hack as soon as we can.

   for (const char* id : extension_misc::kHangoutsExtensionIds) {
     if (extension_id == id)
       return true;
   }
+#endif  // OS_CHROMEOS
 
   return false;
 }