Added UMA statistics for changing the active window via click or touch events.

ui/aura/window.cc

Index: ui/aura/window.cc
diff --git a/ui/aura/window.cc b/ui/aura/window.cc
index 69bddfdc77219efb3630e5455df8d1975138c1df..2ced9089a95908525dbd6ecd2f794025e3ce1ec9 100644
--- a/ui/aura/window.cc
+++ b/ui/aura/window.cc
@@ -202,9 +202,11 @@ Window::Window(WindowDelegate* delegate)
 }
 
 Window::~Window() {
-  if (layer()->owner() == this)
-    layer()->CompleteAllAnimations();
-  layer()->SuppressPaint();
+  if (layer()) {

[danakj, 2015/06/03 22:02:50]

Not having a layer means you made a Window but didn't call Init() on it. Fix the
callsite?

+    if (layer()->owner() == this)
+      layer()->CompleteAllAnimations();
+    layer()->SuppressPaint();
+  }
 
   // Let the delegate know we're in the processing of destroying.
   if (delegate_)
@@ -260,9 +262,11 @@ Window::~Window() {
   }
   prop_map_.clear();
 
-  // The layer will either be destroyed by |layer_owner_|'s dtor, or by whoever
-  // acquired it.
-  layer()->set_delegate(NULL);
+  if (layer()) {
+    // The layer will either be destroyed by |layer_owner_|'s dtor, or by
+    // whoever acquired it.
+    layer()->set_delegate(NULL);
+  }
   DestroyLayer();
 }