[ash-md] Improves smoothness with many windows in overview

ash/common/wm/overview/window_grid.cc

Index: ash/common/wm/overview/window_grid.cc
diff --git a/ash/common/wm/overview/window_grid.cc b/ash/common/wm/overview/window_grid.cc
index 60b9412915a08aae7ddcd0e5c77990309b5fc052..04a9e0e8cf17049c1f9a59989b67c8c896a2c883 100644
--- a/ash/common/wm/overview/window_grid.cc
+++ b/ash/common/wm/overview/window_grid.cc
@@ -97,6 +97,10 @@ const float kCardAspectRatio = 4.0f / 3.0f;
 // landscape orientation).
 const int kMinCardsMajor = 3;
 
+// Hiding windows headers can be resource intensive. Only hide the headers when

[tdanderson, 2016/07/18 16:26:58]

nit: windows->window

[varkha, 2016/07/19 00:29:07]

Done.

+// the number of windows in this grid is less or equal than this number.
+const int kMaxWindowsCountToHideHeader = 10;
+
 const int kOverviewSelectorTransitionMilliseconds = 250;
 
 // The color and opacity of the screen shield in overview.
@@ -446,6 +450,9 @@ void WindowGrid::PrepareForOverview() {
 void WindowGrid::PositionWindowsMD(bool animate) {
   if (window_list_.empty())
     return;
+  const bool hide_header = window_list_.size() <= kMaxWindowsCountToHideHeader;
+  for (auto* window : window_list_)
+    window->set_hide_header(hide_header);
   gfx::Rect total_bounds =
       root_window_->ConvertRectToScreen(wm::GetDisplayWorkAreaBoundsInParent(
           root_window_->GetChildByShellWindowId(