Improve check for whether _NET_ACTIVE_WINDOW is supported

ui/base/x/x11_util.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file defines utility functions for X11 (Linux only). This code has been
 // ported from XCB since we can't use XCB on Ubuntu while its 32-bit support
 // remains woefully incomplete.
 
 #include "ui/base/x/x11_util.h"
 
@@ skipping 84 matching lines @@
                             max_length, // max length to get
                             False,      // deleted
                             AnyPropertyType,
                             type,
                             format,
                             num_items,
                             &remaining_bytes,
                             property);
 }
 
+bool SupportsEWMH() {
+  static bool supports_ewmh = false;
+  static bool supports_ewmh_cached = false;

[Daniel Erat, 2014/09/23 15:32:41]

i was going to say that i'm not sure how i feel about caching this (what if the
window manager is replaced?), but i guess we were already getting this wrong by
caching whether _NET_ACTIVE_WINDOW is supported, so it's not a huge deal. :-/

i think that the right fix here would be to watch for _NET_SUPPORTING_WM_CHECK
property changes on the root window (see e.g. X11DesktopHandler's monitoring of
PropertyNotify events on the root for _NET_ACTIVE_WINDOW), but it's probably not
worth the effort.

+  if (!supports_ewmh_cached) {
+    supports_ewmh_cached = true;
+
+    int wm_window = 0u;
+    if (!GetIntProperty(GetX11RootWindow(),
+                        "_NET_SUPPORTING_WM_CHECK",
+                        &wm_window)) {
+      supports_ewmh = false;
+      return false;
+    }
+
+    // It's possible that a window manager started earlier in this X session
+    // left a stale _NET_SUPPORTING_WM_CHECK property when it was replaced by a
+    // non-EWMH window manager, so we trap errors in the following requests to
+    // avoid crashes (issue 23860).
+
+    // EWMH requires the supporting-WM window to also have a
+    // _NET_SUPPORTING_WM_CHECK property pointing to itself (to avoid a stale
+    // property referencing an ID that's been recycled for another window), so
+    // we check that too.
+    gfx::X11ErrorTracker err_tracker;
+    int wm_window_property = 0;
+    bool result = GetIntProperty(
+        wm_window, "_NET_SUPPORTING_WM_CHECK", &wm_window_property);
+    supports_ewmh = !err_tracker.FoundNewError() &&
+                    result &&
+                    wm_window_property == wm_window;
+  }
+
+  return supports_ewmh;
+}
+
 bool GetWindowManagerName(std::string* wm_name) {
   DCHECK(wm_name);
+  if (!SupportsEWMH())
+    return false;
+
   int wm_window = 0;
   if (!GetIntProperty(GetX11RootWindow(),
                       "_NET_SUPPORTING_WM_CHECK",
                       &wm_window)) {
     return false;
   }
 
-  // It's possible that a window manager started earlier in this X session left
-  // a stale _NET_SUPPORTING_WM_CHECK property when it was replaced by a
-  // non-EWMH window manager, so we trap errors in the following requests to
-  // avoid crashes (issue 23860).
-
-  // EWMH requires the supporting-WM window to also have a
-  // _NET_SUPPORTING_WM_CHECK property pointing to itself (to avoid a stale
-  // property referencing an ID that's been recycled for another window), so we
-  // check that too.
   gfx::X11ErrorTracker err_tracker;
-  int wm_window_property = 0;
-  bool result = GetIntProperty(
-      wm_window, "_NET_SUPPORTING_WM_CHECK", &wm_window_property);
-  if (err_tracker.FoundNewError() || !result ||
-      wm_window_property != wm_window) {
-    return false;
-  }
-
-  result = GetStringProperty(
+  bool result = GetStringProperty(
       static_cast<XID>(wm_window), "_NET_WM_NAME", wm_name);
   return !err_tracker.FoundNewError() && result;
 }
 
 // A process wide singleton that manages the usage of X cursors.
 class XCursorCache {
  public:
   XCursorCache() {}
   ~XCursorCache() {
     Clear();
@@ skipping 1128 matching lines @@
   // TODO(erg): Actually doing this correctly would require pulling out xrandr,
   // which we don't even do in the desktop screen yet.
   ::XDisplay* display = gfx::GetXDisplay();
   ::Screen* screen = DefaultScreenOfDisplay(display);
   int width = WidthOfScreen(screen);
   int height = HeightOfScreen(screen);
   return window_rect.size() == gfx::Size(width, height);
 }
 
 bool WmSupportsHint(XAtom atom) {
+  if (!SupportsEWMH())
+    return false;
+
   std::vector<XAtom> supported_atoms;
   if (!GetAtomArrayProperty(GetX11RootWindow(),
                             "_NET_SUPPORTED",
                             &supported_atoms)) {
     return false;
   }
 
   return std::find(supported_atoms.begin(), supported_atoms.end(), atom) !=
       supported_atoms.end();
 }
@@ skipping 143 matching lines @@
       << "request_code " << static_cast<int>(error_event.request_code) << ", "
       << "minor_code " << static_cast<int>(error_event.minor_code)
       << " (" << request_str << ")";
 }
 
 // ----------------------------------------------------------------------------
 // End of x11_util_internal.h
 
 
 }  // namespace ui