Add UMA to track the number of live URLRequests.

net/url_request/url_request_context.cc

Index: net/url_request/url_request_context.cc
diff --git a/net/url_request/url_request_context.cc b/net/url_request/url_request_context.cc
index 0ec1db63efcd31e5648fe898b009bf4dda0b5730..55c82aa905690b1e739d468ca66b0f3809904476 100644
--- a/net/url_request/url_request_context.cc
+++ b/net/url_request/url_request_context.cc
@@ -9,6 +9,7 @@
 #include "base/compiler_specific.h"
 #include "base/debug/alias.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ -51,7 +52,8 @@ URLRequestContext::URLRequestContext()
       url_requests_(new std::set<const URLRequest*>),
       enable_brotli_(false),
       check_cleartext_permitted_(false),
-      name_(nullptr) {
+      name_(nullptr),
+      largest_outstanding_requests_count_seen_(0) {
   base::trace_event::MemoryDumpManager::GetInstance()->RegisterDumpProvider(
       this, "URLRequestContext", base::ThreadTaskRunnerHandle::Get());
 }
@@ -122,6 +124,20 @@ void URLRequestContext::set_cookie_store(CookieStore* cookie_store) {
   cookie_store_ = cookie_store;
 }
 
+void URLRequestContext::InsertURLRequest(const URLRequest* request) {
+  url_requests_->insert(request);
+  if (url_requests_->size() > largest_outstanding_requests_count_seen_) {
+    largest_outstanding_requests_count_seen_ = url_requests_->size();

[xunjieli, 2017/04/25 21:21:20]

Matt: sorry, I might be missing something. How do I modify the tracking variable
(|largest_outstanding_requests_count_seen_|) while keeping InsertURLRequest() a
const method?

Thanks!

[mmenke, 2017/04/25 21:50:48]

I assume this doesn't build because InsertURLRequest is not const?

I had assumed that since this was modifying url_requests_, we had non-const
access to the URLRequestContext, but I guess we store it in a unique_ptr just to
get around this issue?  That seems weird....  I'd suggest just making this
mutable instead.

Sorry that I didn't realize that earlier.  This solution would have worked with
your original CL, but I didn't realize the unique_ptr magic.  I think combining
this with set insertion is prettier, anyways, though.

+    UMA_HISTOGRAM_COUNTS_1M("Net.URLRequestContext.OutstandingRequests",
+                            largest_outstanding_requests_count_seen_);
+  }
+}
+
+void URLRequestContext::RemoveURLRequest(const URLRequest* request) {
+  DCHECK_EQ(1u, url_requests_->count(request));
+  url_requests_->erase(request);
+}
+
 void URLRequestContext::AssertNoURLRequests() const {
   int num_requests = url_requests_->size();
   if (num_requests != 0) {