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

ash/common/ash_switches.cc

Index: ash/common/ash_switches.cc
diff --git a/ash/common/ash_switches.cc b/ash/common/ash_switches.cc
index 6cf8ab45249e643bf5f7a9a73f0818ce1d937bec..3211e2aa3e61afb2e20679761b955965aa1738ca 100644
--- a/ash/common/ash_switches.cc
+++ b/ash/common/ash_switches.cc
@@ -98,6 +98,16 @@ const char kAshMaterialDesignDisabled[] = "disabled";
 const char kAshMaterialDesignEnabled[] = "enabled";
 const char kAshMaterialDesignExperimental[] = "experimental";
 
+// Specifies a maximum number of preview windows in overview mode that still
+// allows using mask layers to hide the original window header and use rounded
+// corners.
+const char kAshMaxWindowsToUseMaskInOverview[] = "ash-max-previews-to-use-mask";
+
+// Specifies a maximum number of preview windows in overview mode that still
+// allows using alpha shapes to hide the original window header.
+const char kAshMaxWindowsToUseShapeInOverview[] =
+    "ash-max-previews-to-use-shape";
+
 // Specifies the layout mode and offsets for the secondary display for
 // testing. The format is "<t|r|b|l>,<offset>" where t=TOP, r=RIGHT,
 // b=BOTTOM and L=LEFT. For example, 'r,-100' means the secondary display