Measure mojo::DataPipe creation time on the ServiceWorker thread.

We've seen some anecdotal evidence in local testing that mojo::DataPipe
creation can sometimes take milliseconds to complete.  Currently there
is a pipe created on the ServiceWorker thread for certain FetchEvent
respondWith() code paths.  This histogram will help us determine if
this is introducing jank on the service worker thread.

Bug: 888045
Change-Id: I5f36da2dfbde4bd561c605336949e475f45ecb43
Reviewed-on: https://chromium-review.googlesource.com/1239274Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593302}

third_party/blink/renderer/modules/service_worker/fetch_respond_with_observer.cc

@@ -7,6 +7,7 @@
 #include <memory>
 #include <utility>
 
+#include "base/metrics/histogram_macros.h"
 #include "services/network/public/mojom/fetch_api.mojom-blink.h"
 #include "services/network/public/mojom/request_context_frame_type.mojom-blink.h"
 #include "third_party/blink/public/platform/modules/service_worker/web_service_worker_response.h"
@@ -287,12 +288,15 @@ void FetchRespondWithObserver::OnResponseFulfilled(
       return;
     }
     // Handle the stream response body.
+    base::TimeTicks start_pipe_creation = base::TimeTicks::Now();
     mojo::DataPipe pipe;
     if (!pipe.consumer_handle.is_valid()) {
       OnResponseRejected(ServiceWorkerResponseError::kDataPipeCreationFailed);
       return;
     }
     DCHECK(pipe.producer_handle.is_valid());
+    UMA_HISTOGRAM_TIMES("ServiceWorker.FetchRespondWithDataPipeCreation.Time",
+                        base::TimeTicks::Now() - start_pipe_creation);
 
     std::unique_ptr<WebServiceWorkerStreamHandle> body_stream_handle =
         std::make_unique<WebServiceWorkerStreamHandle>(

tools/metrics/histograms/histograms.xml

@@ -93990,6 +93990,15 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="ServiceWorker.FetchRespondWithDataPipeCreation.Time"
+    units="ms">
+  <owner>wanderview@chromium.org</owner>
+  <summary>
+    Measures how long the service worker thread is blocked creating a
+    mojo::DataPipe during FetchEvent.respondWith() processing.
+  </summary>
+</histogram>
+
 <histogram name="ServiceWorker.ForeignFetch.OriginCount">
   <obsolete>
     Deprecated April 2018.