Allow the default browser check to return "unknown" and reflect that in the UI.

chrome/browser/shell_integration.h

 // Copyright (c) 2006-2008 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.
 
 #ifndef CHROME_BROWSER_SHELL_INTEGRATION_H__
 #define CHROME_BROWSER_SHELL_INTEGRATION_H__
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/ref_counted.h"
 #include "base/string16.h"
 #include "googleurl/src/gurl.h"
 
 class FilePath;
 class MessageLoop;
 
 class ShellIntegration {
  public:
   // Sets Chrome as default browser (only for current user). Returns false if
   // this operation fails.
   static bool SetAsDefaultBrowser();
 
-  // Returns true if this instance of Chrome is the default browser. (Defined
-  // as being the handler for the http/https protocols... we don't want to
-  // report false here if the user has simply chosen to open HTML files in a
-  // text editor and ftp links with a FTP client).
-  static bool IsDefaultBrowser();
+  // On Linux, it may not be possible to determine or set the default browser
+  // on some desktop environments or configurations. So, we use this enum and
+  // not a plain bool. (Note however that if used like a bool, this enum will
+  // have reasonable behavior.)
+  enum DefaultBrowserState {
+    NOT_DEFAULT_BROWSER = 0,
+    IS_DEFAULT_BROWSER,
+    UNKNOWN_DEFAULT_BROWSER
+  };
+
+  // Attempt to determine if this instance of Chrome is the default browser and
+  // return the appropriate state. (Defined as being the handler for HTTP/HTTPS
+  // protocols; we don't want to report "no" here if the user has simply chosen
+  // to open HTML files in a text editor and FTP links with an FTP client.)
+  static DefaultBrowserState IsDefaultBrowser();
 
   // Returns true if Firefox is likely to be the default browser for the current
   // user. This method is very fast so it can be invoked in the UI thread.
   static bool IsFirefoxDefaultBrowser();
 
 #if defined(OS_LINUX)
   // Returns filename for .desktop file based on |url|, sanitized for security.
   static FilePath GetDesktopShortcutFilename(const GURL& url);
 
   // Returns contents for .desktop file based on |template_contents|, |url|
@@ skipping 13 matching lines @@
 
   // Creates a desktop shortcut. It is not guaranteed to exist immediately after
   // returning from this function, because actual file operation is done on the
   // file thread.
   static void CreateDesktopShortcut(const ShortcutInfo& shortcut_info);
 #endif  // defined(OS_LINUX)
 
   // The current default browser UI state
   enum DefaultBrowserUIState {
     STATE_PROCESSING,
-    STATE_DEFAULT,
-    STATE_NOT_DEFAULT
+    STATE_NOT_DEFAULT,
+    STATE_IS_DEFAULT,
+    STATE_UNKNOWN
   };
 
   class DefaultBrowserObserver {
    public:
     // Updates the UI state to reflect the current default browser state.
     virtual void SetDefaultBrowserUIState(DefaultBrowserUIState state) = 0;
     virtual ~DefaultBrowserObserver() {}
   };
   //  A helper object that handles checking if Chrome is the default browser on
   //  Windows and also setting it as the default browser. These operations are
@@ skipping 14 matching lines @@
 
     // Called to notify the worker that the view is gone.
     void ObserverDestroyed();
 
    private:
     // Functions that track the process of checking if Chrome is the default
     // browser.  |ExecuteCheckDefaultBrowser| checks the registry on the file
     // thread.  |CompleteCheckDefaultBrowser| notifies the view to update on the
     // UI thread.
     void ExecuteCheckDefaultBrowser();
-    void CompleteCheckDefaultBrowser(bool is_default);
+    void CompleteCheckDefaultBrowser(DefaultBrowserState state);
 
     // Functions that track the process of setting Chrome as the default
     // browser.  |ExecuteSetAsDefaultBrowser| updates the registry on the file
     // thread.  |CompleteSetAsDefaultBrowser| notifies the view to update on the
     // UI thread.
     void ExecuteSetAsDefaultBrowser();
     void CompleteSetAsDefaultBrowser();
 
     // Updates the UI in our associated view with the current default browser
     // state.
-    void UpdateUI(bool is_default);
+    void UpdateUI(DefaultBrowserState state);
 
     DefaultBrowserObserver* observer_;
 
     MessageLoop* ui_loop_;
     MessageLoop* file_loop_;
 
     DISALLOW_COPY_AND_ASSIGN(DefaultBrowserWorker);
   };
 };
 
 #endif  // CHROME_BROWSER_SHELL_INTEGRATION_H__