[perf] Add more native traces for WebView startup

This change adds traces under
BrowserMainLoop::CreateThreads:PreMainMessageLoopRun().

Bug: 1019793
Change-Id: I89577b30b797af78e19cf6afc0079a264fc1df97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1986906Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: Changwan Ryu <changwan@chromium.org>
Commit-Queue: Oksana Zhuravlova <oksamyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#729585}

android_webview/browser/network_service/aw_proxy_config_monitor.cc

@@ -12,6 +12,7 @@
 #include "base/barrier_closure.h"
 #include "base/bind.h"
 #include "base/no_destructor.h"
+#include "base/trace_event/trace_event.h"
 #include "mojo/public/cpp/bindings/pending_remote.h"
 
 namespace android_webview {
@@ -22,6 +23,7 @@ const char kProxyBypassListSwitch[] = "proxy-bypass-list";
 }  // namespace
 
 AwProxyConfigMonitor::AwProxyConfigMonitor() {
+  TRACE_EVENT0("startup", "AwProxyConfigMonitor");
   proxy_config_service_android_ =
       std::make_unique<net::ProxyConfigServiceAndroid>(
           base::ThreadTaskRunnerHandle::Get(),

content/browser/android/background_sync_network_observer_android.cc

@@ -6,6 +6,7 @@
 
 #include "base/bind.h"
 #include "base/task/post_task.h"
+#include "base/trace_event/trace_event.h"
 #include "content/public/android/content_jni_headers/BackgroundSyncNetworkObserver_jni.h"
 #include "content/public/browser/browser_task_traits.h"
 #include "content/public/browser/service_worker_context.h"
@@ -29,6 +30,8 @@ BackgroundSyncNetworkObserverAndroid::Observer::Create(
 }
 
 void BackgroundSyncNetworkObserverAndroid::Observer::Init() {
+  TRACE_EVENT0("startup",
+               "BackgroundSyncNetworkObserverAndroid::Observer::Init");
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   // Attach a Java BackgroundSyncNetworkObserver object. Its lifetime will be
   // scoped to the lifetime of this object.