Emit warning when touchscreen association fails.

ash/touch/touchscreen_util.cc

Index: ash/touch/touchscreen_util.cc
diff --git a/ash/touch/touchscreen_util.cc b/ash/touch/touchscreen_util.cc
index d6538e38d12be4dcaaf847b6be6e2c2c99d8ebf8..224a06b632edde5099a62067daafa59c12037000 100644
--- a/ash/touch/touchscreen_util.cc
+++ b/ash/touch/touchscreen_util.cc
@@ -274,9 +274,9 @@ void AssociateTouchscreens(
   AssociateToSingleDisplay(&displays, &devices);
 
   for (const DisplayInfo* display : displays)
-    VLOG(1) << "Unmatched display " << display->name();
+    LOG(WARNING) << "Unmatched display " << display->name();
   for (const ui::TouchscreenDevice* device : devices)
-    VLOG(1) << "Unmatched device " << device->name;
+    LOG(WARNING) << "Unmatched device " << device->name;
 }
 
 }  // namespace ash