Figure out the MIME type of shared WebUI resources more efficiently

content/browser/webui/shared_resources_data_source.cc

Index: content/browser/webui/shared_resources_data_source.cc
diff --git a/content/browser/webui/shared_resources_data_source.cc b/content/browser/webui/shared_resources_data_source.cc
index d30e03f6c2ef21922a2c9020c969aea22fa9007a..71a06d272596cc3855783a312d9faef13a45253a 100644
--- a/content/browser/webui/shared_resources_data_source.cc
+++ b/content/browser/webui/shared_resources_data_source.cc
@@ -7,14 +7,13 @@
 #include <stddef.h>
 
 #include "base/containers/hash_tables.h"
+#include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted_memory.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
-#include "base/threading/thread_restrictions.h"
 #include "content/public/common/content_client.h"
 #include "content/public/common/url_constants.h"
-#include "net/base/mime_util.h"
 #include "ui/base/layout.h"
 #include "ui/base/webui/web_ui_util.h"
 #include "ui/resources/grit/webui_resources.h"
@@ -104,13 +103,33 @@ void SharedResourcesDataSource::StartDataRequest(
 
 std::string SharedResourcesDataSource::GetMimeType(
     const std::string& path) const {

[groby-ooo-7-16, 2016/04/29 23:39:15]

I still fail to understand why we couldn't run this on the IO thread right away.
As far as I can tell, StartDataRequest is thread-agnostic, which means we could
just return nullptr  MessageLoopForRequestPath

[Dan Beam, 2016/04/30 00:32:34]

Done.

-  // Requests should not block on the disk!  On POSIX this goes to disk.
-  // http://code.google.com/p/chromium/issues/detail?id=59849
+  if (path.empty())
+    return "text/html";
 
-  base::ThreadRestrictions::ScopedAllowIO allow_io;
-  std::string mime_type;
-  net::GetMimeTypeFromFile(base::FilePath().AppendASCII(path), &mime_type);
-  return mime_type;
+  base::FilePath filepath(path);

[groby-ooo-7-16, 2016/04/29 23:39:16]

I'd minimally prefer getting the extension once (path.Extension()) and then
compare, but not enough to make you do it unless you're bored :)

[Dan Beam, 2016/04/30 00:32:34]

Done.

+  if (filepath.MatchesExtension(".html"))

[Dan Beam, 2016/04/29 22:39:36]

list derived via magic

(`find ui/webui/resources/ ui/views/resources/default_*00_percent/common/
third_party/polymer/v1_0/components-chromium/ -type f | grep -o '\..*$' | sort |
uniq | grep -v gyp | grep -v grd | grep -v gtest | grep -v externs | grep -v
txt`)

+    return "text/html";
+
+  if (filepath.MatchesExtension(".css"))
+    return "text/css";
+
+  if (filepath.MatchesExtension(".js"))
+    return "application/javascript";
+
+  if (filepath.MatchesExtension(".png"))
+    return "image/png";
+
+  if (filepath.MatchesExtension(".gif"))
+    return "image/gif";
+
+  if (filepath.MatchesExtension(".svg"))
+    return "image/svg+xml";
+
+  if (filepath.MatchesExtension(".woff2"))
+    return "application/font-woff2";
+
+  NOTREACHED();

[groby-ooo-7-16, 2016/04/29 23:39:15]

You want to do a CHECK here to force people to notice?

[Dan Beam, 2016/04/30 00:32:34]

Done.

+  return "text/plain";
 }
 
 std::string