Add TRACE_EVENT macros to net.

net/url_request/url_request_http_job.cc

Index: net/url_request/url_request_http_job.cc
diff --git a/net/url_request/url_request_http_job.cc b/net/url_request/url_request_http_job.cc
index 9cc020974e82620b41f77f429e293e92d8e8e7f7..c8209896e9074d57108beacd261c021247a8fd14 100644
--- a/net/url_request/url_request_http_job.cc
+++ b/net/url_request/url_request_http_job.cc
@@ -20,6 +20,7 @@
 #include "base/strings/string_util.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/time/time.h"
+#include "base/trace_event/trace_event.h"
 #include "base/values.h"
 #include "net/base/host_port_pair.h"
 #include "net/base/load_flags.h"
@@ -1062,6 +1063,7 @@ void URLRequestHttpJob::OnHeadersReceivedCallback(int result) {
 }
 
 void URLRequestHttpJob::OnReadCompleted(int result) {
+  TRACE_EVENT0("net", "URLRequestHttpJob::OnReadCompleted");

[mmenke, 2016/03/28 20:46:51]

What do you expect to do with the information you get here?  The covers the
filters, passing data to the embedder, and the whatever the embedder does with
the data...But it only covers the case the read completes asynchronously, and
doesn't cover when the filters or embedder does the exact same thing for
non-HTTP requests.  I suggest more targetted tracing.

[ssid, 2016/03/29 00:33:06]

I am expecting that this data is useful to understand where the memory
allocations are coming from. At least it could tell that the allocation is
related to http request in some way.
I was also hoping that Nick and Charles who have more context about the code
will help me making this complete.
cbentzel@ suggested to ask them.

I am working with statistics for adding trace events rather than  understanding
what are all the possible codepaths possible. I did try with lots of websites
and it turns out that case of read completing asynchronously was allocating more
memory than other cases. I tried to read similar functions in each folder and
add events there as well.

I don't understand when you say more targeted tracing. Do you mean I should add
more trace events in each of these components so that the data is complete? If
so, can you propose a way for me to find points to make this instrumentation
complete.

If I can contact one person in each sub-team of networking and point out these
"important" functions that would be great. I am trying to add trace events based
on statistically large memory using functions.
Can you please suggest any other alternative?

   read_in_progress_ = false;
 
   DCHECK_NE(ERR_IO_PENDING, result);