Linux: Fix Valgrind error in VisitedLinkEventsTest.Coalescense.

I introduced the error in r22193; it shows up when there's no X
server to connect to.  I get a "GLib-GObject-CRITICAL **:
g_object_get: assertion `G_IS_OBJECT (object)' failed" message with
this change, but I'm not sure if it's from my code or if it was
already there, and the tests still pass.

TEST=ran VisitedLinkEventsTest.Coalescense under Valgrind with DISPLAY=:6

Review URL: http://codereview.chromium.org/159753

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@22240 0039d316-1c4b-4281-b951-d872f2087c98

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);
 }

chrome/common/x11_util.cc

@@ -26,6 +26,10 @@
 
 namespace x11_util {
 
+bool XDisplayExists() {
+  return (gdk_display_get_default() != NULL);
+}
+
 Display* GetXDisplay() {
   static Display* display = NULL;
 

chrome/common/x11_util.h

@@ -34,6 +34,8 @@ namespace x11_util {
 
 // These functions cache their results.
 
+// Check if there's an open connection to an X server.
+bool XDisplayExists();
 // Return an X11 connection for the current, primary display.
 Display* GetXDisplay();
 // Return true iff the connection supports X shared memory