Fix flakiness in resource_timing_buffer_full_250

This CL uses document fragments to append scripts faster. Also, we do
not need to wait until onload of one script to begin appending the next.

Bug: 626703, 883837
Change-Id: I0bc010640793d6a7113d404f2838fd5cfe88ab25
Reviewed-on: https://chromium-review.googlesource.com/c/1265901Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598896}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3089,7 +3089,6 @@ crbug.com/863355 [ Mac ] external/wpt/svg/shapes/reftests/pathlength-002.svg [ F
 crbug.com/366559 external/wpt/svg/shapes/reftests/pathlength-003.svg [ Failure ]
 crbug.com/366559 external/wpt/svg/text/reftests/textpath-side-001.svg [ Failure ]
 crbug.com/366559 external/wpt/svg/text/reftests/textpath-shape-001.svg [ Failure ]
-crbug.com/626703 [ Win7 ] external/wpt/resource-timing/resource_timing_buffer_full_eventually.html [ Timeout ]
 crbug.com/626703 external/wpt/svg/rendering/order/z-index.svg [ Failure ]
 crbug.com/626703 external/wpt/web-animations/timing-model/timelines/update-and-send-events.html [ Timeout ]
 crbug.com/626703 external/wpt/console/console-timing-logging-manual.html [ Skip ]
@@ -5293,7 +5292,6 @@ crbug.com/869492 virtual/video-surface-layer/external/wpt/feature-policy/experim
 
 # Sheriff 2018-09-13
 crbug.com/883591 [ Android ] fullscreen/full-screen-inline-split-crash.html [ Pass Crash ]
-crbug.com/883837 [ Win7 ] http/tests/performance-timing/resource_timing_buffer_full_250.html [ Timeout Pass ]
 
 # Sheriff 2018-09-18
 crbug.com/884445 virtual/unified-autoplay/external/wpt/feature-policy/feature-policy-nested-header-policy-disallowed-for-all.https.sub.html [ Pass Timeout ]

third_party/WebKit/LayoutTests/external/wpt/resource-timing/resource_timing_buffer_full_eventually.html

@@ -16,15 +16,23 @@
         function() {
             // Scripts appended in JS to ensure setResourceTimingBufferSize is called before.
             let counter = performance.getEntriesByType("resource").length;
-            function appendScript() {
-                const src = "resources/empty.js?" + counter;
-                const script = document.createElement('script');
-                script.type = 'text/javascript';
-                script.onload = function() { ++counter; appendScript()};
-                script.src = src;
-                document.body.appendChild(script);
+            function appendScripts() {
+                const documentFragment = document.createDocumentFragment();
+                // Add 100 elements at a time to avoid page reflow every time.
+                let numScriptsAccumulated = 0;
+                while (numScriptsAccumulated < 100) {
+                    const src = "resources/empty.js?" + counter;
+                    const script = document.createElement('script');
+                    script.type = 'text/javascript';
+                    script.src = src;
+                    documentFragment.appendChild(script);
+                    ++counter;
+                    ++numScriptsAccumulated;
+                }
+                document.body.appendChild(documentFragment);
+                t.step_timeout(appendScripts, 20);
             }
-            appendScript();
+            appendScripts();
         });
 </script>
 </body>

third_party/WebKit/LayoutTests/http/tests/performance-timing/resource_timing_buffer_full_250.html

@@ -18,21 +18,16 @@
         function() {
             // Scripts appended in JS to ensure setResourceTimingBufferSize is called before.
             let counter = performance.getEntriesByType("resource").length;
-            function appendScript() {
-                if (counter > default_buffer_size) {
-                    t.step_timeout(function() {
-                        assert_unreached("Got no buffer full event at " + counter + " resources");
-                    }, 100);
-                    return;
-                }
+            const documentFragment = document.createDocumentFragment();
+            while (counter < default_buffer_size) {
                 const src = "../loading/resources/empty.js?" + counter;
                 const script = document.createElement('script');
                 script.type = 'text/javascript';
-                script.onload = function() { ++counter; appendScript()};
                 script.src = src;
-                document.body.appendChild(script);
+                documentFragment.appendChild(script);
+                ++counter;
             }
-            appendScript();
+            document.body.appendChild(documentFragment);
         });
 </script>
 </body>