This is just an idea for how to implement idle_timer which isn't yet feasible...

base/idle_timer.h

Index: base/idle_timer.h
===================================================================
--- base/idle_timer.h	(revision 2086)
+++ base/idle_timer.h	(working copy)
@@ -28,7 +28,9 @@
 #ifndef BASE_IDLE_TIMER_H_
 #define BASE_IDLE_TIMER_H_
 
+#if defined(OS_WIN)
 #include <windows.h>
+#endif  // OS_WIN
 
 #include "base/basictypes.h"
 #include "base/task.h"
@@ -37,7 +39,7 @@
 namespace base {
 
 // Function prototype for GetLastInputInfo.
-typedef BOOL (__stdcall *GetLastInputInfoFunction)(PLASTINPUTINFO plii);
+typedef bool (*GetIdleTimeFunction)(int32* milliseconds);
 
 class IdleTimer {
  public:
@@ -61,8 +63,8 @@
 
  protected:
   // Override the GetLastInputInfo function.
-  void set_last_input_info_fn(GetLastInputInfoFunction function) {
-    get_last_input_info_fn_ = function;
+  void set_idle_time_fn(GetIdleTimeFunction function) {
+    get_idle_time_fn_ = function;
   }
 
  private:
@@ -78,13 +80,26 @@
   // Compute time until idle.  Returns 0 if we are now idle.
   TimeDelta TimeUntilIdle();
 
+#if defined(OS_LINUX)
+  struct XssInfoLazyInstanceTraits {
+    static void New(void* instance);
+    static void Delete(void* instance);
+  };
+  struct XssInfo {
+    bool have_xss;
+    ThreadLocalPointer<XScreenSaverInfo> xss_info;
+  };
+#endif  // OS_LINUX
+
+  static bool DefaultIdleTimeFunction(int32* milliseconds);
+
   TimeDelta idle_interval_;
   bool repeat_;
   Time last_time_fired_;  // The last time the idle timer fired.
                           // will be 0 until the timer fires the first time.
   OneShotTimer<IdleTimer> timer_;
 
-  GetLastInputInfoFunction get_last_input_info_fn_;
+  GetIdleTimeFunction get_idle_time_fn_;
 
   DISALLOW_COPY_AND_ASSIGN(IdleTimer);
 };