[Not for review] Add traces for crbug.com/726626

third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp

Index: third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp
diff --git a/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp b/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp
index a464f19d1283bdba45958c5665c665ec52c8d3cb..d3b3a9bdcdad51d87c46550a1b5a6a01ad2ece72 100644
--- a/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp
+++ b/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp
@@ -15,6 +15,7 @@
 #include "modules/serviceworkers/ServiceWorkerGlobalScope.h"
 #include "platform/bindings/ScriptState.h"
 #include "platform/bindings/V8PrivateProperty.h"
+#include "platform/instrumentation/tracing/TraceEvent.h"
 #include "platform/loader/fetch/ResourceTimingInfo.h"
 #include "platform/network/NetworkUtils.h"
 #include "platform/wtf/PtrUtil.h"
@@ -81,6 +82,7 @@ FetchEvent::FetchEvent(ScriptState* script_state,
           ExecutionContext::From(script_state),
           this,
           PreloadResponseProperty::kPreloadResponse)) {
+  TRACE_EVENT0("ServiceWorker", "FetchEvent::FetchEvent");
   if (!navigation_preload_sent)
     preload_response_property_->ResolveWithUndefined();
 
@@ -113,19 +115,43 @@ void FetchEvent::OnNavigationPreloadResponse(
     ScriptState* script_state,
     std::unique_ptr<WebURLResponse> response,
     std::unique_ptr<WebDataConsumerHandle> data_consume_handle) {
+  TRACE_EVENT0("ServiceWorker", "FetchEvent::OnNavigationPreloadResponse");
   if (!script_state->ContextIsValid())
     return;
   DCHECK(preload_response_property_);
   DCHECK(!preload_response_);
   ScriptState::Scope scope(script_state);
   preload_response_ = std::move(response);
-  FetchResponseData* response_data =
-      data_consume_handle
-          ? FetchResponseData::CreateWithBuffer(new BodyStreamBuffer(
-                script_state, new BytesConsumerForDataConsumerHandle(
-                                  ExecutionContext::From(script_state),
-                                  std::move(data_consume_handle))))
-          : FetchResponseData::Create();
+  FetchResponseData* response_data;
+  {
+    if (data_consume_handle) {
+      BytesConsumerForDataConsumerHandle* bytes_consumer;
+      {
+        TRACE_EVENT0("ServiceWorker",
+                     "FetchEvent::OnNavigationPreloadResponse "
+                     "BytesConsumerForDataConsumerHandle");
+        bytes_consumer = new BytesConsumerForDataConsumerHandle(
+            ExecutionContext::From(script_state),
+            std::move(data_consume_handle));
+      }
+      BodyStreamBuffer* buffer;
+      {
+        TRACE_EVENT0(
+            "ServiceWorker",
+            "FetchEvent::OnNavigationPreloadResponse BodyStreamBuffer");
+        buffer = new BodyStreamBuffer(script_state, bytes_consumer);
+      }
+      TRACE_EVENT0("ServiceWorker",
+                   "FetchEvent::OnNavigationPreloadResponse "
+                   "FetchResponseData::CreateWithBuffer");
+      response_data = FetchResponseData::CreateWithBuffer(buffer);
+    } else {
+      TRACE_EVENT0(
+          "ServiceWorker",
+          "FetchEvent::OnNavigationPreloadResponse FetchResponseData::Create");
+      response_data = FetchResponseData::Create();
+    }
+  }
   Vector<KURL> url_list(1);
   url_list[0] = preload_response_->Url();
   response_data->SetURLList(url_list);
@@ -138,12 +164,23 @@ void FetchEvent::OnNavigationPreloadResponse(
   for (const auto& header : headers) {
     response_data->HeaderList()->Append(header.key, header.value);
   }
-  FetchResponseData* tainted_response =
-      NetworkUtils::IsRedirectResponseCode(preload_response_->HttpStatusCode())
-          ? response_data->CreateOpaqueRedirectFilteredResponse()
-          : response_data->CreateBasicFilteredResponse();
-  preload_response_property_->Resolve(
-      Response::Create(ExecutionContext::From(script_state), tainted_response));
+  FetchResponseData* tainted_response;
+  {
+    TRACE_EVENT0(
+        "ServiceWorker",
+        "FetchEvent::OnNavigationPreloadResponse CreateBasicFilteredResponse");
+    tainted_response =
+        NetworkUtils::IsRedirectResponseCode(
+            preload_response_->HttpStatusCode())
+            ? response_data->CreateOpaqueRedirectFilteredResponse()
+            : response_data->CreateBasicFilteredResponse();
+  }
+  {
+    TRACE_EVENT0("ServiceWorker",
+                 "FetchEvent::OnNavigationPreloadResponse Resolve");
+    preload_response_property_->Resolve(Response::Create(
+        ExecutionContext::From(script_state), tainted_response));
+  }
 }
 
 void FetchEvent::OnNavigationPreloadError(