[inspector] Flush explicitly after sending resumed event

'resumed' events are sent to the renderer from V8 and stored in a queue.
We didn't flush this queue previously, meaning these events would sit in
the queue until another message coincidentally flushed the queue.

Under some circumstances, the resumed event would not get flushed and
the UI would still be in a paused state, even when JS had resumed.

Bug: chromium:1044989
Change-Id: I5d92fcc0a40d4e3816501da98f6be8a46f227e0f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2023563Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66041}

src/inspector/v8-debugger-agent-impl.cc

@@ -1665,6 +1665,7 @@ void V8DebuggerAgentImpl::didPause(
 void V8DebuggerAgentImpl::didContinue() {
   clearBreakDetails();
   m_frontend.resumed();
+  m_frontend.flush();
 }
 
 void V8DebuggerAgentImpl::breakProgram(