Reduce the size of the fullscreen window on activation loss only if the window being activated is …

ui/views/win/hwnd_message_handler.h

Index: ui/views/win/hwnd_message_handler.h
diff --git a/ui/views/win/hwnd_message_handler.h b/ui/views/win/hwnd_message_handler.h
index 8a114ebee1be90095386ac833f8c4b6937830880..8ca2b1231be5950bc23daf29ae6b1c111ee21592 100644
--- a/ui/views/win/hwnd_message_handler.h
+++ b/ui/views/win/hwnd_message_handler.h
@@ -8,6 +8,7 @@
 #include <windows.h>
 
 #include <stddef.h>
+#include <map>
 #include <memory>
 #include <set>
 #include <vector>
@@ -105,6 +106,14 @@ const int WM_NCUAHDRAWFRAME = 0xAF;
     switch(dwMsgMapID) { \
       case 0:
 
+// This message is posted when our window is activated on the monitor
+// where there is a fullscreen window owned by us. The handler for
+// this message reduces the size of the fullscreen window by 1 px. This is
+// to workaround a bug in the taskbar where it treats all windows owned by
+// a thread on a monitor as fullscreen windows if one of the windows in there
+// is a full screen window. The bug does not occur across monitors.
+const int WM_CUSTOM_MESSAGE_HANDLE_BACKGROUND_FULLSCREEN = WM_USER + 1;
+
 // An object that handles messages for a HWND that implements the views
 // "Custom Frame" look. The purpose of this class is to isolate the windows-
 // specific message handling from the code that wraps it. It is intended to be
@@ -368,6 +377,9 @@ class VIEWS_EXPORT HWNDMessageHandler :
     // word of WPARAM could be set when the window is minimized or restored.
     CR_MESSAGE_HANDLER_EX(WM_NCACTIVATE, OnNCActivate)
 
+    CR_MESSAGE_HANDLER_EX(WM_CUSTOM_MESSAGE_HANDLE_BACKGROUND_FULLSCREEN,
+        OnBackgroundFullscreen)
+
     // This list is in _ALPHABETICAL_ order! OR I WILL HURT YOU.
     CR_MSG_WM_ACTIVATEAPP(OnActivateApp)
     CR_MSG_WM_APPCOMMAND(OnAppCommand)
@@ -459,6 +471,7 @@ class VIEWS_EXPORT HWNDMessageHandler :
   LRESULT OnTouchEvent(UINT message, WPARAM w_param, LPARAM l_param);
   void OnWindowPosChanging(WINDOWPOS* window_pos);
   void OnWindowPosChanged(WINDOWPOS* window_pos);
+  LRESULT OnBackgroundFullscreen(UINT message, WPARAM w_param, LPARAM l_param);
 
   // Receives Windows Session Change notifications.
   void OnSessionChange(WPARAM status_code);
@@ -517,6 +530,12 @@ class VIEWS_EXPORT HWNDMessageHandler :
   void SetBoundsInternal(const gfx::Rect& bounds_in_pixels,
                          bool force_size_changed);
 
+  // Checks if there is a full screen window on the same monitor as the
+  // |window| which is becoming active. If yes then we reduce the size of the
+  // fullscreen window by 1 px to ensure that maximized windows on the same
+  // monitor don't draw over the taskbar.
+  void CheckAndHandleBackgroundFullscreenOnMonitor(HWND window);
+
   HWNDMessageHandlerDelegate* delegate_;
 
   std::unique_ptr<FullscreenHandler> fullscreen_handler_;
@@ -660,6 +679,12 @@ class VIEWS_EXPORT HWNDMessageHandler :
   // The factory used with BEGIN_SAFE_MSG_MAP_EX.
   base::WeakPtrFactory<HWNDMessageHandler> weak_factory_;
 
+  // This is a map of the HMONITOR to full screeen window handle.
+  typedef std::map<HMONITOR, HWND> FullscreenWindowMonitorMap;
+  static FullscreenWindowMonitorMap* fullscreen_monitor_map_;
+  // This holds the number of HWNDMessageHandler instances currently active.
+  static int32_t instance_count_;
+
   DISALLOW_COPY_AND_ASSIGN(HWNDMessageHandler);
 };