Collect some metrics on nosniff. There is some concern that respecting this ...

chrome/browser/renderer_host/buffered_resource_handler.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 "chrome/browser/renderer_host/buffered_resource_handler.h"
 
+#include "base/histogram.h"
 #include "net/base/mime_sniffer.h"
 #include "chrome/browser/renderer_host/download_throttling_resource_handler.h"
 #include "chrome/browser/renderer_host/resource_dispatcher_host.h"
 
+namespace {
+
+void RecordSnifferMetrics(bool sniffing_blocked,
+                          bool we_would_like_to_sniff,
+                          const std::string& mime_type) {
+  static BooleanHistogram nosniff_usage(L"nosniff.usage");
+  nosniff_usage.SetFlags(kUmaTargetedHistogramFlag);
+  nosniff_usage.AddBoolean(sniffing_blocked);
+
+  if (sniffing_blocked) {
+    static BooleanHistogram nosniff_otherwise(L"nosniff.otherwise");
+    nosniff_otherwise.SetFlags(kUmaTargetedHistogramFlag);
+    nosniff_otherwise.AddBoolean(we_would_like_to_sniff);
+
+    static BooleanHistogram nosniff_empty_mime_type(L"nosniff.empty_mime_type");
+    nosniff_empty_mime_type.SetFlags(kUmaTargetedHistogramFlag);
+    nosniff_empty_mime_type.AddBoolean(mime_type.empty());
+  }
+}
+
+}  // namespace
+
 BufferedResourceHandler::BufferedResourceHandler(ResourceHandler* handler,
                                                  ResourceDispatcherHost* host,
                                                  URLRequest* request)
     : real_handler_(handler),
       host_(host),
       request_(request),
       bytes_read_(0),
       sniff_content_(false),
       should_buffer_(false),
       buffering_(false),
@@ skipping 64 matching lines @@
   return real_handler_->OnReadCompleted(request_id, bytes_read);
 }
 
 bool BufferedResourceHandler::DelayResponse() {
   std::string mime_type;
   request_->GetMimeType(&mime_type);
 
   std::string content_type_options;
   request_->GetResponseHeaderByName("x-content-type-options",
                                     &content_type_options);
-  if (content_type_options != "nosniff" &&
-      net::ShouldSniffMimeType(request_->url(), mime_type)) {
+
+  const bool sniffing_blocked = (content_type_options == "nosniff");
+  const bool we_would_like_to_sniff =
+      net::ShouldSniffMimeType(request_->url(), mime_type);
+
+  RecordSnifferMetrics(sniffing_blocked, we_would_like_to_sniff, mime_type);
+
+  if (!sniffing_blocked && we_would_like_to_sniff) {
     // We're going to look at the data before deciding what the content type
     // is.  That means we need to delay sending the ResponseStarted message
     // over the IPC channel.
     sniff_content_ = true;
     LOG(INFO) << "To buffer: " << request_->url().spec();
     return true;
   }
 
   if (ShouldBuffer(request_->url(), mime_type)) {
     // This is a temporary fix for the fact that webkit expects to have
@@ skipping 112 matching lines @@
     real_handler_ = download_handler;
   }
   return real_handler_->OnResponseStarted(request_id, response_);
 }
 
 bool BufferedResourceHandler::DidBufferEnough(int bytes_read) {
   const int kRequiredLength = 256;
 
   return bytes_read >= kRequiredLength;
 }