Add timestamp property to WebTransport created/closed events

This is needed to show the events Waterfall.
I will implement the front end side later on.

Devtools for WebTransport design doc:https://bit.ly/3ig8BLi

Bug: 1152290
Change-Id: I7913c46961f911b0a3f9e8bab44c7e023b4abbd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2576862Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834464}

third_party/blink/public/devtools_protocol/browser_protocol.pdl

@@ -5507,6 +5507,8 @@ domain Network
       RequestId transportId
       # WebTransport request URL.
       string url
+      # Timestamp.
+      MonotonicTime timestamp
       # Request initiator.
       optional Initiator initiator
 
@@ -5514,6 +5516,8 @@ domain Network
     parameters
       # WebTransport identifier.
       RequestId transportId
+      # Timestamp.
+      MonotonicTime timestamp
 
   experimental type PrivateNetworkRequestPolicy extends string
     enum

third_party/blink/renderer/core/inspector/inspector_network_agent.cc

@@ -1684,7 +1684,8 @@ void InspectorNetworkAgent::WebTransportCreated(
   if (!current_stack_trace) {
     GetFrontend()->webTransportCreated(
         IdentifiersFactory::SubresourceRequestId(transport_id),
-        UrlWithoutFragment(request_url).GetString());
+        UrlWithoutFragment(request_url).GetString(),
+        base::TimeTicks::Now().since_origin().InSecondsF());
     return;
   }
 
@@ -1695,12 +1696,15 @@ void InspectorNetworkAgent::WebTransportCreated(
   initiator_object->setStack(std::move(current_stack_trace));
   GetFrontend()->webTransportCreated(
       IdentifiersFactory::SubresourceRequestId(transport_id),
-      UrlWithoutFragment(request_url).GetString(), std::move(initiator_object));
+      UrlWithoutFragment(request_url).GetString(),
+      base::TimeTicks::Now().since_origin().InSecondsF(),
+      std::move(initiator_object));
 }
 
 void InspectorNetworkAgent::WebTransportClosed(uint64_t transport_id) {
   GetFrontend()->webTransportClosed(
-      IdentifiersFactory::SubresourceRequestId(transport_id));
+      IdentifiersFactory::SubresourceRequestId(transport_id),
+      base::TimeTicks::Now().since_origin().InSecondsF());
 }
 
 Response InspectorNetworkAgent::enable(Maybe<int> total_buffer_size,