Add PathService::RemoveOverride to clear path overrides.

base/path_service.h

Index: base/path_service.h
diff --git a/base/path_service.h b/base/path_service.h
index e835a1f34e6b4ddd3c4f313145c30c5cc04ad0fb..d710e595d82db2fc53b579f6f4da0520ada4824a 100644
--- a/base/path_service.h
+++ b/base/path_service.h
@@ -46,6 +46,10 @@ class BASE_EXPORT PathService {
                                         const FilePath& path,
                                         bool create);
 
+  // Removes an override for a special directory or file. Returns true if there
+  // was an override to remove or false if none was present.

[jar (doing other things), 2012/09/15 02:01:20]

nit: If this is meant to only be used for testing, then you should probably
comment about such.  It is nicer to make this method private, and then friend
the tests that use it, so you can enforce it.

+  static bool RemoveOverride(int key);
+
   // To extend the set of supported keys, you can register a path provider,
   // which is just a function mirroring PathService::Get.  The ProviderFunc
   // returns false if it cannot provide a non-empty path for the given key.