Revert "Fix SitePerProcessMouseWheelHitTestBrowserTest.* tests on Win official."

This reverts commit 871421fc.

Reason for revert: this change hasn't fixed the failing tests.

Original change's description:
> Fix SitePerProcessMouseWheelHitTestBrowserTest.* tests on Win official.
> 
> https://chromium-review.googlesource.com/865558 fixes this flaky tests
> on win7_chromium_rel_ng, but it only waits for dispatching of the
> first wheel event before sending the others.
> 
> This cl makes sure that each wheel event gets dispatched before sending
> the next one.
> 
> I haven't been able to reproduce the bug on my local windows official
> build but I suspect that after using async wheel targeting for wheel
> events some of the wheel events in RunTest get coalesced to each other
> before getting dispatched.
> 
> Bug: 800822
> Change-Id: Id693ef3beff19daf08c3e11c2119b2bf90ef6737
> Reviewed-on: https://chromium-review.googlesource.com/893803
> Reviewed-by: James MacLean <wjmaclean@chromium.org>
> Reviewed-by: Nasko Oskov <nasko@chromium.org>
> Commit-Queue: Sahel Sharifymoghaddam <sahel@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#533002}

TBR=kenrb@chromium.org,nasko@chromium.org,wjmaclean@chromium.org,sahel@chromium.org

Change-Id: I62fa9ba2075ffaf7ac685dad56af84bd06237214
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 800822
Reviewed-on: https://chromium-review.googlesource.com/894998Reviewed-by: Sahel Sharifymoghaddam <sahel@chromium.org>
Commit-Queue: Sahel Sharifymoghaddam <sahel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533311}

content/browser/site_per_process_hit_test_browsertest.cc

@@ -1600,7 +1600,6 @@ class SitePerProcessMouseWheelHitTestBrowserTest
 
     InputEventAckWaiter waiter(expected_target->GetRenderWidgetHost(),
                                blink::WebInputEvent::kMouseWheel);
-    waiter.Reset();
     SendMouseWheel(pos);
     waiter.Wait();
 
@@ -1610,9 +1609,7 @@ class SitePerProcessMouseWheelHitTestBrowserTest
     EXPECT_TRUE(msg_queue.WaitForMessage(&reply));
     EXPECT_EQ("\"scroll: 1\"", reply);
 
-    waiter.Reset();
     SendMouseWheel(pos);
-    waiter.Wait();
 
     // If async_wheel_events is disabled, this time only the wheel handler
     // fires, since even numbered scrolls are prevent-defaulted. If it is
@@ -1627,9 +1624,7 @@ class SitePerProcessMouseWheelHitTestBrowserTest
       EXPECT_EQ("\"scroll: 2\"", reply);
     }
 
-    waiter.Reset();
     SendMouseWheel(pos);
-    waiter.Wait();
 
     // Odd number of wheels, expect both wheel and scroll handlers to fire
     // again.