Allow relative paths to external extension files for some providers, error out for others.

chrome/browser/extensions/external_registry_extension_loader_win.cc

Index: chrome/browser/extensions/external_registry_extension_loader_win.cc
diff --git a/chrome/browser/extensions/external_registry_extension_loader_win.cc b/chrome/browser/extensions/external_registry_extension_loader_win.cc
index 11c35f18e071246b99357012513a228288149bd4..594da26e5bafe39ef3e0371301607168c6b802ab 100644
--- a/chrome/browser/extensions/external_registry_extension_loader_win.cc
+++ b/chrome/browser/extensions/external_registry_extension_loader_win.cc
@@ -50,8 +50,17 @@ void ExternalRegistryExtensionLoader::LoadOnFileThread() {
     key_path.append(L"\\");
     key_path.append(iterator.Name());
     if (key.Open(kRegRoot, key_path.c_str(), KEY_READ)) {
-      std::wstring extension_path;
-      if (key.ReadValue(kRegistryExtensionPath, &extension_path)) {
+      std::wstring extension_path_str;
+      if (key.ReadValue(kRegistryExtensionPath, &extension_path_str)) {
+        FilePath extension_path(extension_path_str);
+        if (!extension_path.IsAbsolute()) {
+          LOG(ERROR) << "Path " << extension_path_str
+                     << " needs to be absolute in key "
+                     << key_path;
+          ++iterator;
+          continue;
+        }
+
         std::wstring extension_version;
         if (key.ReadValue(kRegistryExtensionVersion, &extension_version)) {
           std::string id = WideToASCII(iterator.Name());
@@ -79,7 +88,7 @@ void ExternalRegistryExtensionLoader::LoadOnFileThread() {
               WideToASCII(extension_version));
           prefs->SetString(
               id + "." + ExternalExtensionProviderImpl::kExternalCrx,
-              extension_path);
+              extension_path_str);
         } else {
           // TODO(erikkay): find a way to get this into about:extensions
           LOG(ERROR) << "Missing value " << kRegistryExtensionVersion