Fix mac raciness with initial needs begin frame state

content/browser/renderer_host/render_widget_host_view_mac_unittest.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #include <Cocoa/Cocoa.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <tuple>
@@ skipping 931 matching lines @@
   MockRenderWidgetHostImpl* host =
       new MockRenderWidgetHostImpl(&delegate, process_host, routing_id);
   RenderWidgetHostViewMac* view = new RenderWidgetHostViewMac(host, false);
   process_host->sink().ClearMessages();
 
   // Send an initial wheel event with NSEventPhaseBegan to the view.
   NSEvent* event1 = MockScrollWheelEventWithPhase(@selector(phaseBegan), 0);
   [view->cocoa_view() scrollWheel:event1];
   ASSERT_EQ(1U, process_host->sink().message_count());
 
+  // Flush and clear other messages (e.g. begin frames) the RWHVMac also sends.
+  base::RunLoop().RunUntilIdle();
+  process_host->sink().ClearMessages();
+
   // Send an ACK for the first wheel event, so that the queue will be flushed.
   InputEventAck ack(blink::WebInputEvent::MouseWheel,
                     INPUT_EVENT_ACK_STATE_CONSUMED);
   std::unique_ptr<IPC::Message> response(
       new InputHostMsg_HandleInputEvent_ACK(0, ack));
   host->OnMessageReceived(*response);
 
   // Post the NSEventPhaseEnded wheel event to NSApp and check whether the
   // render view receives it.
   NSEvent* event2 = MockScrollWheelEventWithPhase(@selector(phaseEnded), 0);
   [NSApp postEvent:event2 atStart:NO];
   base::RunLoop().RunUntilIdle();
-  ASSERT_EQ(2U, process_host->sink().message_count());
+  ASSERT_EQ(1U, process_host->sink().message_count());
 
   // Clean up.
   host->ShutdownAndDestroyWidget(true);
 }
 
 TEST_F(RenderWidgetHostViewMacTest,
        IgnoreEmptyUnhandledWheelEventWithWheelGestures) {
   // Initialize the view associated with a MockRenderWidgetHostImpl, rather than
   // the MockRenderProcessHost that is set up by the test harness which mocks
   // out |OnMessageReceived()|.
@@ skipping 599 matching lines @@
   // Verify that this IPC is asking for no monitoring or immediate updates.
   InputMsg_RequestCompositionUpdate::Read(composition_request_msg_for_child,
                                           &child_msg_params);
   is_child_msg_for_immediate_request = std::get<0>(child_msg_params);
   is_child_msg_for_monitor_request = std::get<1>(child_msg_params);
   EXPECT_FALSE(is_child_msg_for_immediate_request);
   EXPECT_FALSE(is_child_msg_for_monitor_request);
 }
 
 }  // namespace content