Links in platform apps should open in the system default browser.

chrome/browser/shell_integration_linux.h

Index: chrome/browser/shell_integration_linux.h
diff --git a/chrome/browser/shell_integration_linux.h b/chrome/browser/shell_integration_linux.h
index 6918910b429730c4d2cc83d9c5db9a2561114601..012310cd6ccf68525b21ee791a0161b9b79b2004 100644
--- a/chrome/browser/shell_integration_linux.h
+++ b/chrome/browser/shell_integration_linux.h
@@ -59,6 +59,9 @@ bool CreateDesktopShortcut(const ShellIntegration::ShortcutInfo& shortcut_info,
 void DeleteDesktopShortcuts(const FilePath& profile_path,
                             const std::string& extension_id);
 
+// Launch the default system browser to navigate url.
+void LaunchDefaultBrowser(const GURL& url);
+
 }  // namespace ShellIntegrationLinux
 
 #endif  // CHROME_BROWSER_SHELL_INTEGRATION_LINUX_H_