Adds tracing to investigate infinite calls to SetAutoHideBehavior

ash/common/shelf/wm_shelf.cc

Index: ash/common/shelf/wm_shelf.cc
diff --git a/ash/common/shelf/wm_shelf.cc b/ash/common/shelf/wm_shelf.cc
index ffa969a7951bb3b2b558d3940930246e965b9a2d..e439381929be6836869bb732665d2bf36d8c5d57 100644
--- a/ash/common/shelf/wm_shelf.cc
+++ b/ash/common/shelf/wm_shelf.cc
@@ -166,6 +166,19 @@ int WmShelf::PrimaryAxisValue(int horizontal, int vertical) const {
 void WmShelf::SetAutoHideBehavior(ShelfAutoHideBehavior auto_hide_behavior) {
   DCHECK(shelf_layout_manager_);
 
+  // Force a stack dump when this method is invoked too frequently.
+  // This block is here temporary to help investigate http://crbug.com/665093 .
+  constexpr int kAutoHideRepeatInterval = 10000;
+  constexpr int kMaxAutoHideChangesIn10Seconds = 100;
+  if ((base::TimeTicks::Now() - time_last_auto_hide_change_).InMilliseconds() <
+      kAutoHideRepeatInterval) {
+    if (++count_auto_hide_changes_ > kMaxAutoHideChangesIn10Seconds)
+      CHECK(false);
+  } else {
+    count_auto_hide_changes_ = 0;
+  }
+  time_last_auto_hide_change_ = base::TimeTicks::Now();
+
   if (auto_hide_behavior_ == auto_hide_behavior)
     return;