Linux: Fix Valgrind error in VisitedLinkEventsTest.Coalescense.

chrome/browser/gtk/browser_window_gtk.cc

Index: chrome/browser/gtk/browser_window_gtk.cc
diff --git a/chrome/browser/gtk/browser_window_gtk.cc b/chrome/browser/gtk/browser_window_gtk.cc
index e4f7155a6cca3c7a2ee6adc222e0cd573cbf75ca..ccfc556fa0bd058f12d40e9aa996b8d253474145 100644
--- a/chrome/browser/gtk/browser_window_gtk.cc
+++ b/chrome/browser/gtk/browser_window_gtk.cc
@@ -1194,8 +1194,12 @@ GtkWindow* BrowserWindowGtk::GetBrowserWindowForXID(XID xid) {
 // static
 void BrowserWindowGtk::RegisterUserPrefs(PrefService* prefs) {
   bool custom_frame_default = false;
-  if (!prefs->HasPrefPath(prefs::kUseCustomChromeFrame))
+  // Avoid checking the window manager if we're not connected to an X server (as
+  // is the case in Valgrind tests).
+  if (x11_util::XDisplayExists() &&
+      !prefs->HasPrefPath(prefs::kUseCustomChromeFrame)) {
     custom_frame_default = GetCustomFramePrefDefault();
+  }
   prefs->RegisterBooleanPref(
       prefs::kUseCustomChromeFrame, custom_frame_default);
 }