[web] Fix error in ClickDebouncer when using VoiceOver (#174046)

When using VoiceOver, clicking the button through `ctrl+opt+space`
causes the browser to send `pointerdown`, `pointerup` and `click` events
successively within the same event loop. This case wasn't handled
correct by the recent `ClickDebouncer` change here:
https://github.com/flutter/flutter/pull/172995

More details:

We currently wait until the end of the event loop to set the
`ClickDebouncer`'s state. When other events arrive before the end of the
event loop, they expect the `state` to already be set.

The fix is to set the `state` immediately to allow events to be queued
right away, but still keep the debouncing delayed until the end of the
event loop so that Safari continues to work correctly (issue:
https://github.com/flutter/flutter/issues/172180)

Fixes https://github.com/flutter/flutter/issues/173741
https://dart.googlesource.com/external/github.com/flutter/flutter/+/8df5257785eafe93aac2b367f819aa71e21c297a

DEPS

diff --git a/DEPS b/DEPS
index ee91643..0ffc60a 100644
--- a/DEPS
+++ b/DEPS
@@ -231,7 +231,7 @@
 deps = {
   'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '7e75e84ab4ac00db198c1a1cc86138fd511cbace',
 
-  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '8d937c05b105f6888dd429a67b4c66a99d3012ea',
+  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '8df5257785eafe93aac2b367f819aa71e21c297a',
 
   'flutter/engine/src/flutter/third_party/depot_tools':
   Var('chromium_git') + '/chromium/tools/depot_tools.git' + '@' + '580b4ff3f5cd0dcaa2eacda28cefe0f45320e8f7',

commits.json

diff --git a/commits.json b/commits.json
index 101d428..439bfd1 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
-  "flutter":"8d937c05b105f6888dd429a67b4c66a99d3012ea",
+  "flutter":"8df5257785eafe93aac2b367f819aa71e21c297a",
   "flutter/engine/src/flutter/third_party/dart":"7e75e84ab4ac00db198c1a1cc86138fd511cbace"
 }
\ No newline at end of file