Fix black background when locking with fullscreen window:

base/time.h

Index: base/time.h
diff --git a/base/time.h b/base/time.h
index 78d7456b68ae273c3bf27e8aaf93cd3742efe02c..e2aeacede779c7e89d2a986c6007ac07e8efbabc 100644
--- a/base/time.h
+++ b/base/time.h
@@ -17,6 +17,9 @@
 // Time::Now() may actually decrease or jump).  But note that TimeTicks may
 // "stand still", for example if the computer suspended.
 //
+// TimeFactory can be used to override values returned by Time::Now and
+// TimeTicks::Now for test purposes.
+//
 // These classes are represented as only a 64-bit value, so they can be
 // efficiently passed by value.
 
@@ -638,6 +641,25 @@ inline TimeTicks TimeDelta::operator+(TimeTicks t) const {
   return TimeTicks(t.ticks_ + delta_);
 }
 
+// TimeFactory ----------------------------------------------------------------
+
+// This class should be subclassed to provide test values for Time::Now and
+// TimeTicks::Now. Subclass instance should register itself by setting
+// |instance_| fields.
+class BASE_EXPORT TimeFactory {
+ public:
+  // Substitutes value for Time::Now().
+  virtual Time TimeNow() = 0;
+  // Substitutes value for TimeTicks::Now()
+  virtual TimeTicks TimeTicksNow() = 0;
+
+  // Returns instance of |TimeFactory|. If null, system time routines are used.
+  static TimeFactory* instance() { return instance_; }
+ protected:
+  // Implementation of TimeFactory (set by implementing subclasses).
+  static TimeFactory* instance_;
+};
+
 }  // namespace base
 
 #endif  // BASE_TIME_H_