WebSocketStream: Make backpressure-receive.any.js work again

The web test
external/wpt/websockets/stream/tentative/backpressure-receive.any.js
started failing on Windows 10 with the switch to Python 3. It appears
some additional buffering is happening in the OS. As a workaround,
split the large message that is supposed to be delayed by backpressure
into 16 parts.

BUG=1155106

Change-Id: Ifa2b04e4857f3c537721735cec187f610c053d99
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2613853
Commit-Queue: Domenic Denicola <domenic@chromium.org>
Auto-Submit: Adam Rice <ricea@chromium.org>
Reviewed-by: Domenic Denicola <domenic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841571}

third_party/blink/web_tests/TestExpectations

@@ -51,11 +51,6 @@ crbug.com/1048761 external/wpt/infrastructure/server/wpt-server-wpt-flags.sub.ht
 # WPT Test harness doesn't deal with finding an about:blank ref test
 crbug.com/1066130 external/wpt/infrastructure/assumptions/blank.html [ Failure ]
 
-# When running under Python 3 on Windows, this test fails to activate backpressure.
-crbug.com/1155106 external/wpt/websockets/stream/tentative/backpressure-receive.any.html [ Failure ]
-crbug.com/1155106 external/wpt/websockets/stream/tentative/backpressure-receive.any.worker.html [ Failure ]
-crbug.com/1155106 external/wpt/websockets/stream/tentative/backpressure-receive.any.sharedworker.html [ Failure ]
-
 # Favicon is not supported by run_web_tests.
 external/wpt/fetch/metadata/favicon.https.sub.html [ Skip ]
 

third_party/blink/web_tests/external/wpt/websockets/handlers/send-backpressure_wsh.py

@@ -9,7 +9,12 @@ import time
 # this number too large will result in false positives, when it takes more than
 # 2 seconds to transmit the message anyway. This number was arrived at by
 # trial-and-error.
-MESSAGE_SIZE = 16 * 1024 * 1024
+MESSAGE_SIZE = 1024 * 1024
+
+# With Windows 10 and Python 3, the OS will buffer an entire message in memory
+# and return from send() immediately, even if it is very large. To work around
+# this problem, send multiple messages.
+MESSAGE_COUNT = 16
 
 
 def web_socket_do_extra_handshake(request):
@@ -26,8 +31,10 @@ def web_socket_transfer_data(request):
     # 3 is complete. time.time() can go backwards.
     start_time = time.time()
 
-    # The large message that will be blocked by backpressure.
+    # The large messages that will be blocked by backpressure.
+    for i in range(MESSAGE_COUNT):
         request.ws_stream.send_message(b' ' * MESSAGE_SIZE, binary=True)
 
     # Report the time taken to send the large message.
-    request.ws_stream.send_message(six.text_type(time.time() - start_time), binary=False)
+    request.ws_stream.send_message(six.text_type(time.time() - start_time),
+                                   binary=False)

third_party/blink/web_tests/external/wpt/websockets/stream/tentative/backpressure-receive.any.js

@@ -5,6 +5,7 @@
 
 // Allow for this much timer jitter.
 const JITTER_ALLOWANCE_MS = 200;
+const LARGE_MESSAGE_COUNT = 16;
 
 // This test works by using a server WebSocket handler which sends a large
 // message, and then sends a second message with the time it measured the first
@@ -22,8 +23,10 @@ promise_test(async t => {
   // Skip the empty message used to fill the readable queue.
   await reader.read();
 
-  // Skip the large message.
+  // Skip the large messages.
+  for (let i = 0; i < LARGE_MESSAGE_COUNT; ++i) {
     await reader.read();
+  }
 
   // Read the time it took.
   const { value, done } = await reader.read();