base: Add missing "virtual" keyword and OVERRIDE to some methods.

base/process_util_posix.cc

Index: base/process_util_posix.cc
diff --git a/base/process_util_posix.cc b/base/process_util_posix.cc
index 018296c5628b341310b395f548cb961df35e8df0..e148f11e58ecfa13a446ac96941ef4dbbfc79adb 100644
--- a/base/process_util_posix.cc
+++ b/base/process_util_posix.cc
@@ -1268,7 +1268,8 @@ class BackgroundReaper : public PlatformThread::Delegate {
         timeout_(timeout) {
   }
 
-  void ThreadMain() {
+  // Overridden from PlatformThread::Delegate:
+  virtual void ThreadMain() OVERRIDE {
     WaitForChildToDie();
     delete this;
   }