Collect some metrics on nosniff. There is some concern that respecting this header causes more harm than good.

R=darin


Review URL: http://codereview.chromium.org/18214

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@8257 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 43 insertions, 2 deletions

diff --git a/base/histogram.h b/base/histogram.h
index f56d05f..8b4bded 100644
--- a/base/histogram.h
+++ b/base/histogram.h
@@ -370,6 +370,18 @@ class LinearHistogram : public Histogram {
   DISALLOW_EVIL_CONSTRUCTORS(LinearHistogram);
 };
 
+//------------------------------------------------------------------------------
+
+// BooleanHistogram is a histogram for booleans.
+class BooleanHistogram : public LinearHistogram {
+ public:
+  BooleanHistogram(const wchar_t* name) : LinearHistogram(name, 0, 2, 3) {}
+
+  virtual void AddBoolean(bool value) { Add(value ? 1 : 0); }
+
+ private:
+  DISALLOW_EVIL_CONSTRUCTORS(BooleanHistogram);
+};
 
 //------------------------------------------------------------------------------
 // This section provides implementation for ThreadSafeHistogram.
diff --git a/chrome/browser/renderer_host/buffered_resource_handler.cc b/chrome/browser/renderer_host/buffered_resource_handler.cc
index 7630dd1..14f6934 100644
--- a/chrome/browser/renderer_host/buffered_resource_handler.cc
+++ b/chrome/browser/renderer_host/buffered_resource_handler.cc
@@ -4,10 +4,33 @@
 
 #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)
@@ -92,8 +115,14 @@ bool BufferedResourceHandler::DelayResponse() {
   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.