Reland r57575 - Remove the default argument from RegKey::Open.

base/registry.h

Index: base/registry.h
diff --git a/base/registry.h b/base/registry.h
index 6199362b2668156340435ea39cb864594981e6e9..0b6c00c36818463844dc92c76e9ab144594c8911 100644
--- a/base/registry.h
+++ b/base/registry.h
@@ -29,7 +29,7 @@ class RegKey {
   bool CreateWithDisposition(HKEY rootkey, const wchar_t* subkey,
                              DWORD* disposition, REGSAM access);
 
-  bool Open(HKEY rootkey, const wchar_t* subkey, REGSAM access = KEY_READ);
+  bool Open(HKEY rootkey, const wchar_t* subkey, REGSAM access);
 
   // Creates a subkey or open it if it already exists.
   bool CreateKey(const wchar_t* name, REGSAM access);