content/browser: Move more files into the content namespace.

content/browser/mime_registry_message_filter.cc

Index: content/browser/mime_registry_message_filter.cc
diff --git a/content/browser/mime_registry_message_filter.cc b/content/browser/mime_registry_message_filter.cc
index ef7e9947185e652e802f70b853a9d06cbce3dcf8..e29e1fac484d12ba429025f1fd6a7a07c982e26d 100644
--- a/content/browser/mime_registry_message_filter.cc
+++ b/content/browser/mime_registry_message_filter.cc
@@ -7,7 +7,7 @@
 #include "content/common/mime_registry_messages.h"
 #include "net/base/mime_util.h"
 
-using content::BrowserThread;
+namespace content {
 
 MimeRegistryMessageFilter::MimeRegistryMessageFilter() {
 }
@@ -51,3 +51,5 @@ void MimeRegistryMessageFilter::OnGetPreferredExtensionForMimeType(
     const std::string& mime_type, FilePath::StringType* extension) {
   net::GetPreferredExtensionForMimeType(mime_type, extension);
 }
+
+}  // namespace content