DevTools: Fix a flaky test that relies on attach timings

Properly order setAutoAttach and onceAttachedToTarget.

Change-Id: I15462ac670a691c1bad1859d3b1846e86d21bfce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1943133
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Auto-Submit: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720161}

third_party/blink/web_tests/TestExpectations

@@ -4414,7 +4414,6 @@ crbug.com/757165 [ Win ] http/tests/devtools/console/console-links-in-errors-wit
 crbug.com/757165 [ Win ] http/tests/devtools/extensions/extensions-panel.js [ Skip ]
 crbug.com/757165 [ Win ] http/tests/devtools/sources/ui-source-code-metadata.js [ Skip ]
 crbug.com/757165 [ Win ] http/tests/misc/client-hints-accept-meta-preloader.html [ Skip ]
-crbug.com/757165 [ Win ] inspector-protocol/debugger/debugger-evaluate-in-worker-while-pause-in-page.js [ Skip ]
 crbug.com/757165 [ Win ] paint/invalidation/filters/filter-repaint-accelerated-child-with-filter-child.html [ Skip ]
 crbug.com/757165 [ Win ] paint/invalidation/filters/filter-repaint-on-accelerated-layer.html [ Skip ]
 crbug.com/757165 [ Win ] virtual/gpu/fast/canvas/canvas-filter-modified-save-restore.html [ Skip ]

third_party/blink/web_tests/inspector-protocol/debugger/debugger-evaluate-in-worker-while-pause-in-page.js

@@ -9,15 +9,17 @@
   `);
   testRunner.log('Started worker');
 
-  dp.Debugger.enable();
+  await dp.Debugger.enable();
+  const pausedPromise = dp.Debugger.oncePaused();
   dp.Runtime.evaluate({expression: 'debugger;' });
-  await dp.Debugger.oncePaused();
+  await pausedPromise;
   testRunner.log(`Paused on 'debugger;'`);
 
-  dp.Target.setAutoAttach({autoAttach: true, waitForDebuggerOnStart: false,
+  const attachedPromise = dp.Target.onceAttachedToTarget();
+  await dp.Target.setAutoAttach({autoAttach: true, waitForDebuggerOnStart: false,
                            flatten: true});
 
-  const messageObject = await dp.Target.onceAttachedToTarget();
+  const messageObject = await attachedPromise;
   testRunner.log('Worker created');
   testRunner.log('didConnectToWorker');