[base] Always return true from ProcessNextWindowsMessage if there were sent messages

This was already the intent of the method but it incorrectly returned
false if there were sent messages but ProcessMessageHelper(msg)
returned false (i.e. |msg| was kMsgHaveWork and there were no others).

Extracted from https://chromium-review.googlesource.com/c/chromium/src/+/2185757/2

R=fdoray@chromium.org

Bug: 1075960
Change-Id: I3a60b01598b15f3deea5aabd83112cf2ace5cabb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2185831
Commit-Queue: Gabriel Charette <gab@chromium.org>
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#768509}

base/message_loop/message_pump_win.cc

@@ -456,7 +456,7 @@ bool MessagePumpForUI::ProcessNextWindowsMessage() {
   // dispatches the message and returns false. We return true in this
   // case to ensure that the message loop peeks again instead of calling
   // MsgWaitForMultipleObjectsEx.
-  bool sent_messages_in_queue = false;
+  bool more_work_is_plausible = false;
   {
     // Individually trace ::GetQueueStatus and ::PeekMessage because sampling
     // profiler is hinting that we're spending a surprising amount of time with
@@ -468,7 +468,7 @@ bool MessagePumpForUI::ProcessNextWindowsMessage() {
                  "MessagePumpForUI::ProcessNextWindowsMessage GetQueueStatus");
     DWORD queue_status = ::GetQueueStatus(QS_SENDMESSAGE);
     if (HIWORD(queue_status) & QS_SENDMESSAGE)
-      sent_messages_in_queue = true;
+      more_work_is_plausible = true;
   }
 
   MSG msg;
@@ -483,19 +483,19 @@ bool MessagePumpForUI::ProcessNextWindowsMessage() {
     static const auto kAdditionalFlags =
         FeatureList::IsEnabled(kNoYieldFromNativePeek) ? PM_NOYIELD : 0x0;
 
-    // PeekMessage can run a message if |sent_messages_in_queue|, trace that and
+    // PeekMessage can run a message if there are sent messages, trace that and
     // emit the boolean param to see if it ever janks independently (ref.
     // comment on GetQueueStatus).
     TRACE_EVENT1("base",
                  "MessagePumpForUI::ProcessNextWindowsMessage PeekMessage",
-                 "sent_messages_in_queue", sent_messages_in_queue);
+                 "sent_messages_in_queue", more_work_is_plausible);
     has_msg = ::PeekMessage(&msg, nullptr, 0, 0,
                             kAdditionalFlags | PM_REMOVE) != FALSE;
   }
   if (has_msg)
-    return ProcessMessageHelper(msg);
+    more_work_is_plausible |= ProcessMessageHelper(msg);
 
-  return sent_messages_in_queue;
+  return more_work_is_plausible;
 }
 
 bool MessagePumpForUI::ProcessMessageHelper(const MSG& msg) {