Add full support for filesystem URLs.

net/base/mime_sniffer.cc

Index: net/base/mime_sniffer.cc
diff --git a/net/base/mime_sniffer.cc b/net/base/mime_sniffer.cc
index b0b6d03d1b6881a8e78a5d33457d98234e1e8c73..4ef21610368d55816b75e2eb179bafcb8c405e89 100644
--- a/net/base/mime_sniffer.cc
+++ b/net/base/mime_sniffer.cc
@@ -567,12 +567,12 @@ bool ShouldSniffMimeType(const GURL& url, const std::string& mime_type) {
   if (!should_sniff_counter)
     should_sniff_counter =
         UMASnifferHistogramGet("mime_sniffer.ShouldSniffMimeType2", 3);
-  // We are willing to sniff the mime type for HTTP, HTTPS, and FTP
   bool sniffable_scheme = url.is_empty() ||
                           url.SchemeIs("http") ||
                           url.SchemeIs("https") ||
                           url.SchemeIs("ftp") ||
-                          url.SchemeIsFile();
+                          url.SchemeIsFile() ||
+                          url.SchemeIsFileSystem();
   if (!sniffable_scheme) {
     should_sniff_counter->Add(1);
     return false;