Protobuf for Traffic Annotation and first use by a URLFetcher.

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index 928d1af83dcbf8f870f59b487989fa3cc2708cd9..09c5431b4a76b6161555c081c1ece54b837885e6 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -358,6 +358,7 @@ component("net") {
 
   public_deps = [
     ":net_quic_proto",
+    ":traffic_annotation",
     "//crypto",
     "//crypto:platform",
   ]
@@ -2395,6 +2396,7 @@ static_library("test_support") {
     "test/url_request/url_request_mock_data_job.h",
     "test/url_request/url_request_slow_download_job.cc",
     "test/url_request/url_request_slow_download_job.h",
+    "traffic_annotation/network_traffic_annotation_test_helper.h",
     "url_request/test_url_fetcher_factory.cc",
     "url_request/test_url_fetcher_factory.h",
     "url_request/url_request_test_util.cc",
@@ -2420,6 +2422,7 @@ static_library("test_support") {
   ]
 
   public_deps = [
+    ":traffic_annotation",
     "//base",
     "//base/test:test_support",
     "//crypto",
@@ -2975,6 +2978,13 @@ source_set("simple_quic_tools") {
   ]
 }
 
+source_set("traffic_annotation") {
+  sources = [
+    "traffic_annotation/network_traffic_annotation.h",
+  ]
+  deps = []
+}
+
 if (!is_ios) {
   executable("quic_client") {
     sources = [