Fix -full fallback for diff updates (M56).

chrome/installer/mini_installer/regkey.h

Index: chrome/installer/mini_installer/regkey.h
diff --git a/chrome/installer/mini_installer/regkey.h b/chrome/installer/mini_installer/regkey.h
index f323b7c697fe69bb3c9f355c0098b4220ee99fba..86dbf8b17475e3a3c1fd368f20cb0e246f2c4eb4 100644
--- a/chrome/installer/mini_installer/regkey.h
+++ b/chrome/installer/mini_installer/regkey.h
@@ -55,11 +55,19 @@ class RegKey {
   HKEY key_;
 };  // class RegKey
 
-
-// Helper function to get the RegKey associated with the "client state" of
-// the given |app_guid|.
-bool OpenClientStateKey(HKEY root_key, const wchar_t* app_guid,
-                        REGSAM access, RegKey* key);
+// Initializes |key| with the desired |access| to |app_guid|'s Clients key.

[huangs, 2017/01/31 17:40:04]

I see this function in code search already; need to Sync?

Meanwhile, it looks like:
- configuration.cc is the only user of this.
- |app_guid| is only useful for GOOGLE_CHROME_BUILD.
- |app_guid| is always |google_update::kAppGuid|.

I'd recommend moving OpenClientKey() and OpenClientStateKey() to local
namespace{} inside configuration.cc, with hard-coded values. But this is beyond
scope of CL.

[grt (UTC plus 2), 2017/02/02 08:17:16]

Yeah, I don't really like this either. OpenClientStateKey is used outside of
configuration.cc, so I'm going to leave these as-is for now.

+// Returns ERROR_SUCCESS on success, or a Windows error code on failure.
+LONG OpenClientsKey(HKEY root_key,
+                    const wchar_t* app_guid,
+                    REGSAM access,
+                    RegKey* key);
+
+// Initializes |key| with the desired |access| to |app_guid|'s ClientState key.
+// Returns ERROR_SUCCESS on success, or a Windows error code on failure.
+LONG OpenClientStateKey(HKEY root_key,
+                        const wchar_t* app_guid,
+                        REGSAM access,
+                        RegKey* key);
 
 }  // namespace mini_installer