Adding sniffing of MHTML files.

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 bd16462f159b7430508093044786e3b44deccf64..6c845ccb4c957cef5b584bd0398ad1b4c6dcbf0c 100644
--- a/net/base/mime_sniffer.cc
+++ b/net/base/mime_sniffer.cc
@@ -534,15 +534,10 @@ static bool SniffCRX(const char* content,
   };
 
   // Only consider files that have the extension ".crx".
-  static const char kCRXExtension[] = ".crx";
-  // Ignore null by subtracting 1.
-  static const int kExtensionLength = arraysize(kCRXExtension) - 1;
-  if (url.path().rfind(kCRXExtension, std::string::npos, kExtensionLength) ==
-      url.path().size() - kExtensionLength) {
-    counter->Add(1);
-  } else {
+  if (!EndsWith(url.path(), ".crx", true))
     return false;
-  }
+
+  counter->Add(1);
 
   *have_enough_content &= TruncateSize(kBytesRequiredForMagic, &size);
   if (CheckForMagicNumbers(content, size,
@@ -663,6 +658,14 @@ bool SniffMimeType(const char* content, size_t content_size,
                &have_enough_content, result))
     return true;
 
+  // MHTML cannot be easily sniffed as its header might be relatively long
+  // before the "Content-Type: multipart/related".
+  std::string path = url.path();
+  if (EndsWith(path, ".mht", false) || EndsWith(path, ".mhtml", false)) {
+    result->assign("multipart/related");
+    return true;
+  }
+
   // We're not interested in sniffing for magic numbers when the type_hint
   // is application/octet-stream.  Time to bail out.
   if (type_hint == "application/octet-stream")