Adjust our sniffing hueristics to better match Firefox....

net/base/mime_sniffer_unittest.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/basictypes.h"
 #include "googleurl/src/gurl.h"
 #include "net/base/mime_sniffer.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
@@ skipping 63 matching lines @@
       "http://www.example.com/foo",
       "text/plain", "image/gif" },
     { "Gif87a\x1F\x83\x94", sizeof("Gif87a\xAF\x83\x94")-1,
       "http://www.example.com/foo?param=tt.gif",
       "", "application/octet-stream" },
     { "%!PS-Adobe-3.0", sizeof("%!PS-Adobe-3.0")-1,
       "http://www.example.com/foo",
       "text/plain", "text/plain" },
     { "\x89" "PNG\x0D\x0A\x1A\x0A", sizeof("\x89" "PNG\x0D\x0A\x1A\x0A")-1,
       "http://www.example.com/foo",
-      "application/octet-stream", "image/png" },
+      "application/octet-stream", "application/octet-stream" },
     { "\xFF\xD8\xFF\x23\x49\xAF", sizeof("\xFF\xD8\xFF\x23\x49\xAF")-1,
       "http://www.example.com/foo",
       "", "image/jpeg" },
   };
 
   TestArray(tests, arraysize(tests));
 }
 
 TEST(MimeSnifferTest, ChromeExtensionsTest) {
   SnifferTest tests[] = {
@@ skipping 270 matching lines @@
   // Make a large input, with 600 bytes of "x".
   std::string content;
   content.resize(600);
   std::fill(content.begin(), content.end(), 'x');
 
   // content.size() >= kMaxBytesToSniff (512) so the sniff is unambiguous.
   std::string mime_type;
   EXPECT_TRUE(net::SniffMimeType(content.data(), content.size(), GURL(),
                                  "text/xml", &mime_type));
 }