Make streaming upload work with network fallback on service worker

This partially implements whatwg/fetch#1144 and
w3c/ServiceWorker#1560.

ServiceWorkerSubresourceLoader reuses the request body in the original
request in the network fallback case
(ServiceWorkerSubresourceLoader::OnFallback). This is problematic for
a request with streaming upload body, because the body is not copyable.

Ideally we should tee the body as specified in
whatwg/fetch#1144 and
w3c/ServiceWorker#1560, but this CL stops
passing the body to the service worker instead to unblock the origin
trial, assuming that few users care about the streaming body in the
service worker.

Bug: 1165690
Change-Id: Ie1d2d2fd74990b1bf7f9b10e55710a644871cc60
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2712842
Reviewed-by: Matt Falkenhagen <[email protected]>
Reviewed-by: Yoichi Osato <[email protected]>
Reviewed-by: Kinuko Yasuda <[email protected]>
Auto-Submit: Yutaka Hirano <[email protected]>
Commit-Queue: Yutaka Hirano <[email protected]>
Cr-Commit-Position: refs/heads/master@{#857605}

Author: yutakahirano

service-workers/service-worker/fetch-event.https.html

@@ -501,7 +501,7 @@
     const echo_url = '/fetch/api/resources/echo-content.py?ignore';
     const response = await frame.contentWindow.fetch(echo_url, {
         method: 'POST',
-        body: rs
+        body: rs.pipeThrough(new TextEncoderStream())
     });
     const text = await response.text();
     assert_equals(text,
@@ -550,9 +550,10 @@
     const frame = await with_iframe(page_url);
     t.add_cleanup(() => { frame.remove(); });
     const echo_url = '/fetch/api/resources/echo-content.py?use-and-ignore';
-    await promise_rejects_js(t, TypeError, frame.contentWindow.fetch(echo_url, {
+    const w = frame.contentWindow;
+    await promise_rejects_js(t, w.TypeError, w.fetch(echo_url, {
         method: 'POST',
-        body: rs
+        body: rs.pipeThrough(new TextEncoderStream())
     }));
   }, 'FetchEvent#body is a ReadableStream, used and passed to network fallback');