Implement ChromeOS mime type extension mappings.

net/base/mime_util.h

Index: net/base/mime_util.h
diff --git a/net/base/mime_util.h b/net/base/mime_util.h
index 80f440ef3e0adc990e121c2f4a608e40608f7e87..be4bf965ee673819daeabd5f37f7f1494bbeac77 100644
--- a/net/base/mime_util.h
+++ b/net/base/mime_util.h
@@ -166,6 +166,16 @@ NET_EXPORT void AddMultipartFinalDelimiterForUpload(
     const std::string& mime_boundary,
     std::string* post_data);
 
+struct MimeInfo {
+  const char* const mime_type;
+  const char* const extensions;  // comma separated list
+};
+
+// Finds mime type of |ext| from |mappings|.
+const char* FindMimeType(const MimeInfo* mappings,
+                         size_t mappings_len,
+                         const char* ext);
+
 }  // namespace net
 
 #endif  // NET_BASE_MIME_UTIL_H__