Add some histograms for <a ping> requests.

content/browser/loader/detachable_resource_handler.h

Index: content/browser/loader/detachable_resource_handler.h
diff --git a/content/browser/loader/detachable_resource_handler.h b/content/browser/loader/detachable_resource_handler.h
index 2482270b865da4513e36e7ec5084fa88555299a5..25235b6532c0073b09afb4f84f45dd2126b26b35 100644
--- a/content/browser/loader/detachable_resource_handler.h
+++ b/content/browser/loader/detachable_resource_handler.h
@@ -10,9 +10,11 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
+#include "base/timer/elapsed_timer.h"
 #include "base/timer/timer.h"
 #include "content/browser/loader/resource_handler.h"
 #include "content/public/browser/resource_controller.h"
+#include "net/url_request/url_request_status.h"
 
 namespace net {
 class IOBuffer;
@@ -80,6 +82,8 @@ class DetachableResourceHandler : public ResourceHandler,
   virtual void CancelWithError(int error_code) OVERRIDE;
 
  private:
+  void TimedOut();
+
   scoped_ptr<ResourceHandler> next_handler_;
   scoped_refptr<net::IOBuffer> read_buffer_;
 
@@ -88,6 +92,14 @@ class DetachableResourceHandler : public ResourceHandler,
 
   bool is_deferred_;
   bool is_finished_;
+  bool timed_out_;
+
+  bool response_started_;
+  base::ElapsedTimer time_since_start_;
+
+  // The status recorded from OnResponseCompleted. Value is
+  // net::URLRequestStatus::IO_PENDING if OnResponseCompleted is never received.
+  net::URLRequestStatus::Status status_;
 
   DISALLOW_COPY_AND_ASSIGN(DetachableResourceHandler);
 };