Log the error result when observing a registry key fails.

chrome/browser/extensions/external_registry_loader_win.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/extensions/external_registry_loader_win.h"
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
@@ skipping 183 matching lines @@
       BrowserThread::UI, FROM_HERE,
       base::Bind(&ExternalRegistryLoader::CompleteLoadAndStartWatchingRegistry,
                  this));
 }
 
 void ExternalRegistryLoader::CompleteLoadAndStartWatchingRegistry() {
   CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   LoadFinished();
 
   // Start watching registry.
-  if (hklm_key_.Create(HKEY_LOCAL_MACHINE, kRegistryExtensions,
-                       KEY_NOTIFY | KEY_WOW64_32KEY) == ERROR_SUCCESS) {
+  LONG result = ERROR_SUCCESS;
+  if ((result = hklm_key_.Create(HKEY_LOCAL_MACHINE, kRegistryExtensions,
+                                 KEY_NOTIFY | KEY_WOW64_32KEY)) ==
+      ERROR_SUCCESS) {
     base::win::RegKey::ChangeCallback callback =
         base::Bind(&ExternalRegistryLoader::OnRegistryKeyChanged,
                    base::Unretained(this), base::Unretained(&hklm_key_));
     hklm_key_.StartWatching(callback);
   } else {
-    LOG(WARNING) << "Error observing HKLM.";
+    LOG(WARNING) << "Error observing HKLM: " << result;

[lazyboy, 2017/02/15 00:19:56]

Maybe we should remove logging this and keep only the HKCU warning below?

[Wez, 2017/02/15 00:33:21]

Actually it seems like a legitimate error; IIUC correctly the intention of this
code is simply to watch and read from the key(s), so I think we should probably
fix the call-site to try to open the key just for reading.

WDYT?

   }
 
-  if (hkcu_key_.Create(HKEY_CURRENT_USER, kRegistryExtensions, KEY_NOTIFY) ==
-      ERROR_SUCCESS) {
+  if ((result = hkcu_key_.Create(HKEY_CURRENT_USER, kRegistryExtensions,
+                                 KEY_NOTIFY)) == ERROR_SUCCESS) {
     base::win::RegKey::ChangeCallback callback =
         base::Bind(&ExternalRegistryLoader::OnRegistryKeyChanged,
                    base::Unretained(this), base::Unretained(&hkcu_key_));
     hkcu_key_.StartWatching(callback);
   } else {
-    LOG(WARNING) << "Error observing HKCU.";
+    LOG(WARNING) << "Error observing HKCU: " << result;
   }
 }
 
 void ExternalRegistryLoader::OnRegistryKeyChanged(base::win::RegKey* key) {
   // |OnRegistryKeyChanged| is removed as an observer when the ChangeCallback is
   // called, so we need to re-register.
   key->StartWatching(base::Bind(&ExternalRegistryLoader::OnRegistryKeyChanged,
                                 base::Unretained(this), base::Unretained(key)));
 
   BrowserThread::PostTask(
       BrowserThread::FILE, FROM_HERE,
       base::Bind(&ExternalRegistryLoader::UpdatePrefsOnFileThread, this));
 }
 
 void ExternalRegistryLoader::UpdatePrefsOnFileThread() {
   CHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   base::TimeTicks start_time = base::TimeTicks::Now();
   std::unique_ptr<base::DictionaryValue> prefs = LoadPrefsOnFileThread();
   LOCAL_HISTOGRAM_TIMES("Extensions.ExternalRegistryLoaderWinUpdate",
                         base::TimeTicks::Now() - start_time);
   BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
                           base::Bind(&ExternalRegistryLoader::OnUpdated, this,
                                      base::Passed(&prefs)));
 }
 
 }  // namespace extensions