Add GetMimeTypeFromFile to Mojo's network service.

mojo/services/network/network_service_impl.cc

Index: mojo/services/network/network_service_impl.cc
diff --git a/mojo/services/network/network_service_impl.cc b/mojo/services/network/network_service_impl.cc
index 661f7e0cf6f910523c69c04cf840e0633c2e89a6..1b77db3fca2318b2e6b465acaa02d1a52daa2709 100644
--- a/mojo/services/network/network_service_impl.cc
+++ b/mojo/services/network/network_service_impl.cc
@@ -12,6 +12,7 @@
 #include "mojo/services/network/udp_socket_impl.h"
 #include "mojo/services/network/url_loader_impl.h"
 #include "mojo/services/network/web_socket_impl.h"
+#include "net/base/mime_util.h"
 
 namespace mojo {
 
@@ -78,4 +79,13 @@ void NetworkServiceImpl::CreateHttpServer(
                          app_refcount_->Clone(), callback);
 }
 
+void NetworkServiceImpl::GetMimeTypeFromFile(
+    const mojo::String& file_path,
+    const GetMimeTypeFromFileCallback& callback) {
+  std::string mime;
+  net::GetMimeTypeFromFile(
+      base::FilePath::FromUTF8Unsafe(file_path.To<std::string>()), &mime);
+  callback.Run(mime);
+}
+
 }  // namespace mojo