Chrome OS: avoid suspending on lid close when casting is active.

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 532da3e7fd56a71f1e7faec89a07a28f571bab13..6375c8e30c7b92f50314a57c4f01ae8cc19cb867 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -583,6 +583,9 @@ Shell::Shell(ShellDelegate* delegate)
   // We can't do this with a root window listener because XI_HierarchyChanged
   // messages don't have a target window.
   base::MessagePumpX11::Current()->AddObserver(output_configurator());
+
+  MediaCaptureDevicesDispatcher::GetInstance()->AddObserver(
+      output_configurator());
 #endif  // defined(OS_CHROMEOS)
 
 #if defined(OS_CHROMEOS)
@@ -710,6 +713,8 @@ Shell::~Shell() {
   base::MessagePumpX11::Current()->RemoveDispatcherForRootWindow(
       output_configurator());
   base::MessagePumpX11::Current()->RemoveObserver(output_configurator());
+  MediaCaptureDevicesDispatcher::GetInstance()->RemoveObserver(
+      output_configurator());
   display_change_observer_.reset();
 #endif  // defined(OS_CHROMEOS)