Reland "Deflake inspector-protocol/input/dispatchKeyEvent-focus.js"

This reverts commit 4af14ca3c99bd7edbf100e05db93564b7107cc62.

Reason for revert: relanding once the outage is over.

Original change's description:
> Revert "Deflake inspector-protocol/input/dispatchKeyEvent-focus.js"
> 
> This reverts commit 27378e0364b705643275c861f4ba64b70572dff1.
> 
> Reason for revert: Due to Gerrit outage http://crbug.com/872722, we are reverting this CL. Please, re-land it after all clear is given. If you have questions, please ask on the bug. Sorry for the inconvenience.
> 
> Original change's description:
> > Deflake inspector-protocol/input/dispatchKeyEvent-focus.js
> > 
> > The keystrokes injected via Input.dispatchKeyEvent through the browser are
> > racing against Runtime.evaluate in the renderer, so we need to wait for
> > the async completion of the last dispatchKeyEvent before validating the
> > tests results with evaluate.
> > 
> > Bug: 872081
> > Change-Id: Ic5ef41feba6a877c76c05de2e09e019a826756a1
> > Reviewed-on: https://chromium-review.googlesource.com/1168200
> > Reviewed-by: Andrey Lushnikov <lushnikov@chromium.org>
> 
> TBR=dgozman@chromium.org,lushnikov@chromium.org,caseq@chromium.org
> 
> Change-Id: I6f7e8e41eab2c756875103cae24576c37784baf3
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 872081
> Reviewed-on: https://chromium-review.googlesource.com/1169789
> Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>

TBR=dgozman@chromium.org,lushnikov@chromium.org,caseq@chromium.org,tandrii@chromium.org

Change-Id: Ia8e5d3e56d923c31451474969afad7450e8e734d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 872081
Reviewed-on: https://chromium-review.googlesource.com/1170007Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581956}

third_party/WebKit/LayoutTests/inspector-protocol/input/dispatchKeyEvent-focus.js

@@ -36,7 +36,7 @@
       windowsVirtualKeyCode: 9,
       key: 'Tab',
     });
-    dp.Input.dispatchKeyEvent({
+    return dp.Input.dispatchKeyEvent({
       type: 'keyUp',
       windowsVirtualKeyCode: 9,
       key: 'Tab',
@@ -56,7 +56,7 @@
   type('foo');
   typeTab();
   type('bar');
-  typeTab();
+  await typeTab();
   testRunner.log(await session.evaluate(`
     logs.push('================');
     logs.push('value of foo:' + document.getElementById('foo').value);