Revert "Add URLRequest creation stack traces to AssertNoURLRequests crashes."

This caused a regression on Cronet perf tests.  I'll reland with some windows-only ifdefs.  Sadly, our infrastructure makes it easier to revert and reland with modifications than to land another CL, if you have a lot of local branches.

This reverts commit ac0c504b.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Add URLRequest creation stack traces to AssertNoURLRequests crashes.
> 
> We have a top crasher here (Again...), and need to figure out just
> what's going on. Hopefully once we ship the network service, we'll
> never see these crashes again (Well, at least in the network
> process).
> 
> Bug: 800391
> Change-Id: Ifbd45274ac73ca90c7103aea66ba0f7d254c9e6e
> Reviewed-on: https://chromium-review.googlesource.com/916894
> Reviewed-by: Eric Roman <eroman@chromium.org>
> Commit-Queue: Matt Menke <mmenke@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#536575}

TBR=eroman@chromium.org,mmenke@chromium.org

Change-Id: Id648cff17e81452d0203b13d1b4b00a49976a6b8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 800391
Reviewed-on: https://chromium-review.googlesource.com/919401Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536739}

net/url_request/url_request.h

@@ -12,7 +12,6 @@
 #include <vector>
 
 #include "base/debug/leak_tracker.h"
-#include "base/debug/stack_trace.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/optional.h"
@@ -694,12 +693,6 @@ class NET_EXPORT URLRequest : public base::SupportsUserData {
   // called with a response from the server.
   void SetResponseHeadersCallback(ResponseHeadersCallback callback);
 
-  // Stack trace when the URLRequest was created.
-  // TODO(mmenke): Remove once https://crbug.com/800391 is resolved.
-  const base::debug::StackTrace& creation_stack_trace() const {
-    return creation_stack_trace_;
-  }
-
  protected:
   // Allow the URLRequestJob class to control the is_pending() flag.
   void set_is_pending(bool value) { is_pending_ = value; }
@@ -915,11 +908,6 @@ class NET_EXPORT URLRequest : public base::SupportsUserData {
   RequestHeadersCallback request_headers_callback_;
   ResponseHeadersCallback response_headers_callback_;
 
-  // Automatically initialized in constructor to be the stack trace when |this|
-  // is created.
-  // TODO(mmenke): Remove once https://crbug.com/800391 is resolved.
-  const base::debug::StackTrace creation_stack_trace_;
-
   THREAD_CHECKER(thread_checker_);
 
   DISALLOW_COPY_AND_ASSIGN(URLRequest);

net/url_request/url_request_context.cc

@@ -8,7 +8,6 @@
 
 #include "base/compiler_specific.h"
 #include "base/debug/alias.h"
-#include "base/debug/stack_trace.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
@@ -143,12 +142,9 @@ void URLRequestContext::AssertNoURLRequests() const {
     // many we leaked so we have an idea of how bad it is.
     const URLRequest* request = *url_requests_->begin();
     int load_flags = request->load_flags();
-    base::debug::StackTrace creation_stack_trace =
-        request->creation_stack_trace();
     DEBUG_ALIAS_FOR_GURL(url_buf, request->url());
     base::debug::Alias(&num_requests);
     base::debug::Alias(&load_flags);
-    base::debug::Alias(&creation_stack_trace);
     CHECK(false) << "Leaked " << num_requests << " URLRequest(s). First URL: "
                  << request->url().spec().c_str() << ".";
   }