Add trace events around URLLoader/URLLoaderClient.

These can help figure out what happens in the life of a request, as
otherwise it can be hard to figure out which implementation of the
Mojo interfaces are being used.

Change-Id: I24e2e33cd45cf80e936b2feba62c0dab62463e62
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2147162Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759145}

content/renderer/loader/url_loader_client_impl.cc

@@ -238,6 +238,9 @@ void URLLoaderClientImpl::Bind(
 void URLLoaderClientImpl::OnReceiveResponse(
     network::mojom::URLResponseHeadPtr response_head) {
   has_received_response_head_ = true;
+  TRACE_EVENT1("loading", "URLLoaderClientImpl::OnReceiveResponse", "url",
+               last_loaded_url_.possibly_invalid_spec());
+
   if (NeedsStoringMessage()) {
     StoreAndDispatch(
         std::make_unique<DeferredOnReceiveResponse>(std::move(response_head)));

content/renderer/loader/web_url_loader_impl.cc

@@ -773,6 +773,10 @@ void WebURLLoaderImpl::Context::OnStartLoadingResponseBody(
     mojo::ScopedDataPipeConsumerHandle body) {
   if (client_)
     client_->DidStartLoadingResponseBody(std::move(body));
+
+  TRACE_EVENT_WITH_FLOW0(
+      "loading", "WebURLLoaderImpl::Context::OnStartLoadingResponseBody", this,
+      TRACE_EVENT_FLAG_FLOW_IN | TRACE_EVENT_FLAG_FLOW_OUT);
 }
 
 void WebURLLoaderImpl::Context::OnTransferSizeUpdated(int transfer_size_diff) {

services/network/url_loader.cc

@@ -25,6 +25,7 @@
 #include "base/task/thread_pool.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
+#include "base/trace_event/trace_event.h"
 #include "mojo/public/cpp/system/simple_watcher.h"
 #include "net/base/elements_upload_data_stream.h"
 #include "net/base/ip_endpoint.h"
@@ -1676,6 +1677,8 @@ void URLLoader::DeleteSelf() {
 }
 
 void URLLoader::SendResponseToClient() {
+  TRACE_EVENT1("loading", "network::URLLoader::SendResponseToClient", "url",
+               url_request_->url().possibly_invalid_spec());
   url_loader_client_->OnReceiveResponse(std::move(response_));
 
   net::IOBufferWithSize* metadata =

third_party/blink/common/loader/throttling_url_loader.cc

@@ -8,6 +8,7 @@
 #include "base/single_thread_task_runner.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_task_runner_handle.h"
+#include "base/trace_event/trace_event.h"
 #include "net/http/http_status_code.h"
 #include "net/http/http_util.h"
 #include "net/url_request/redirect_util.h"
@@ -529,6 +530,8 @@ void ThrottlingURLLoader::OnReceiveResponse(
   DCHECK_EQ(DEFERRED_NONE, deferred_stage_);
   DCHECK(!loader_completed_);
   DCHECK(deferring_throttles_.empty());
+  TRACE_EVENT1("loading", "ThrottlingURLLoader::OnReceiveResponse", "url",
+               response_url_.possibly_invalid_spec());
 
   // Dispatch BeforeWillProcessResponse().
   if (!throttles_.empty()) {
@@ -672,6 +675,8 @@ void ThrottlingURLLoader::OnStartLoadingResponseBody(
     mojo::ScopedDataPipeConsumerHandle body) {
   DCHECK_EQ(DEFERRED_NONE, deferred_stage_);
   DCHECK(!loader_completed_);
+  TRACE_EVENT1("loading", "ThrottlingURLLoader::OnStartLoadingResponseBody",
+               "url", response_url_.possibly_invalid_spec());
 
   forwarding_client_->OnStartLoadingResponseBody(std::move(body));
 }