ui: Add debug flag to show composited layer borders in ChromeOS UI.

chrome/browser/flag_descriptions.cc

Index: chrome/browser/flag_descriptions.cc
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 01081dfa3c51b068687e20163c994d3edb4367d1..57c4307bd4fede14c590cb3a53a3405abfcef973 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -749,6 +749,20 @@ const char kUiSlowAnimationsName[] = "Slow UI animations";
 
 const char kUiSlowAnimationsDescription[] = "Makes all UI animations slow.";
 
+const char kUiShowCompositedLayerBordersName[] =
+    "Show UI composited layer borders";
+
+const char kUiShowCompositedLayerBordersDescription[] =
+    "Show border around composited layers created by UI.";
+
+const char kUiShowCompositedLayerBordersRenderpass[] = "Renderpass";
+
+const char kUiShowCompositedLayerBordersSurface[] = "Surface";
+
+const char kUiShowCompositedLayerBordersLayer[] = "Layer";
+
+const char kUiShowCompositedLayerBordersAll[] = "All";
+
 #endif  // defined(USE_ASH)
 
 const char kJavascriptHarmonyShippingName[] =