Style cleanup in preparation for auto-linting base/.

base/timer.h

Index: base/timer.h
diff --git a/base/timer.h b/base/timer.h
index a87149e38c6402e0c54e46580635fa14ff22c78c..a6d18bca4ea2b1a5eeb61eac0a955fccbff5f461 100644
--- a/base/timer.h
+++ b/base/timer.h
@@ -85,7 +85,7 @@ class BaseTimer_Helper {
   // We have access to the timer_ member so we can orphan this task.
   class TimerTask : public Task {
    public:
-    TimerTask(TimeDelta delay) : timer_(NULL), delay_(delay) {
+    explicit TimerTask(TimeDelta delay) : timer_(NULL), delay_(delay) {
     }
     virtual ~TimerTask() {}
     BaseTimer_Helper* timer_;