Fix for a long standing bug in Chrome windows with the auto hide taskbar.

chrome/browser/ui/views/chrome_views_delegate.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.
 
 #include "chrome/browser/ui/views/chrome_views_delegate.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
 #include "base/strings/string_util.h"
@@ skipping 72 matching lines @@
   if (!profile) {
     // Use local state for windows that have no explicit profile.
     return g_browser_process->local_state();
   }
   return profile->GetPrefs();
 }
 
 #if defined(OS_WIN)
 bool MonitorHasTopmostAutohideTaskbarForEdge(UINT edge, HMONITOR monitor) {
   APPBARDATA taskbar_data = { sizeof(APPBARDATA), NULL, 0, edge };
+  taskbar_data.hWnd = ::GetForegroundWindow();
 
   // TODO(robliao): Remove ScopedTracker below once crbug.com/462368 is fixed.
   tracked_objects::ScopedTracker tracking_profile(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "462368 MonitorHasTopmostAutohideTaskbarForEdge"));
 
   // MSDN documents an ABM_GETAUTOHIDEBAREX, which supposedly takes a monitor
   // rect and returns autohide bars on that monitor.  This sounds like a good
   // idea for multi-monitor systems.  Unfortunately, it appears to not work at
   // least some of the time (erroneously returning NULL) and there's almost no
   // online documentation or other sample code using it that suggests ways to
-  // address this problem.  So we just use ABM_GETAUTOHIDEBAR and hope the user
-  // only cares about autohide bars on the monitor with the primary taskbar.
-  //
+  // address this problem. We do the following:-
+  // 1. Use the ABM_GETAUTOHIDEBAR message. If it works, i.e. returns a valid
+  //    window we are done.
+  // 2. If the ABM_GETAUTOHIDEBAR message does not work we query the auto hide
+  //    state of the taskbar and then retrieve its position. That call returns
+  //    the edge on which the taskbar is present. If it matches the edge we
+  //    are looking for, we are done.
   // NOTE: This call spins a nested message loop.
   HWND taskbar = reinterpret_cast<HWND>(SHAppBarMessage(ABM_GETAUTOHIDEBAR,
                                                         &taskbar_data));
+  if (!::IsWindow(taskbar)) {
+    APPBARDATA taskbar_data = { sizeof(APPBARDATA), 0, 0, 0};
+    unsigned int taskbar_state = SHAppBarMessage(ABM_GETSTATE,

[sky, 2015/11/22 15:57:19]

All these ole function calls make me nervous that they're going to spin nested
message loops. What thread does this code urn on? Can we run it in the
background?

[ananta, 2015/11/23 19:10:44]

Please see below. The function GetAppbarAutohideEdgesOnWorkerThread which calls
this function runs in a worker thread. If memory serves me right, you did this.
:)

+                                                 &taskbar_data);
+    if (!(taskbar_state & ABS_AUTOHIDE))
+      return false;
+
+    taskbar_data.hWnd = ::FindWindow(L"Shell_TrayWnd", NULL);
+    if (!::IsWindow(taskbar_data.hWnd))
+      return false;
+
+    SHAppBarMessage(ABM_GETTASKBARPOS, &taskbar_data);
+    if (taskbar_data.uEdge == edge)
+      taskbar = taskbar_data.hWnd;
+  }
   return ::IsWindow(taskbar) &&
       (MonitorFromWindow(taskbar, MONITOR_DEFAULTTONULL) == monitor) &&
       (GetWindowLong(taskbar, GWL_EXSTYLE) & WS_EX_TOPMOST);
 }
 
 int GetAppbarAutohideEdgesOnWorkerThread(HMONITOR monitor) {
   DCHECK(monitor);
 
   int edges = 0;
   if (MonitorHasTopmostAutohideTaskbarForEdge(ABE_LEFT, monitor))
@@ skipping 352 matching lines @@
   return content::BrowserThread::GetBlockingPool();
 }
 
 #if !defined(USE_AURA) && !defined(USE_CHROMEOS)
 views::Widget::InitParams::WindowOpacity
 ChromeViewsDelegate::GetOpacityForInitParams(
     const views::Widget::InitParams& params) {
   return views::Widget::InitParams::OPAQUE_WINDOW;
 }
 #endif