re-land the "SourceEventType added to LatencyInfo."

content/browser/renderer_host/render_widget_host_view_mac_unittest.mm

Index: content/browser/renderer_host/render_widget_host_view_mac_unittest.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac_unittest.mm b/content/browser/renderer_host/render_widget_host_view_mac_unittest.mm
index 101493a82577c2c55c873a5eff62884422d0d7d4..7fb728f2e5deead6d309d742bff24bfe39717b1e 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac_unittest.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac_unittest.mm
@@ -903,6 +903,32 @@ TEST_F(RenderWidgetHostViewMacTest, LastWheelEventLatencyInfoExists) {
   host->ShutdownAndDestroyWidget(true);
 }
 
+TEST_F(RenderWidgetHostViewMacTest, SourceEventTypeExistsInLatencyInfo) {
+  // Initialize the view associated with a MockRenderWidgetHostImpl, rather than
+  // the MockRenderProcessHost that is set up by the test harness which mocks
+  // out |OnMessageReceived()|.
+  TestBrowserContext browser_context;
+  MockRenderProcessHost* process_host =
+      new MockRenderProcessHost(&browser_context);
+  process_host->Init();
+  MockRenderWidgetHostDelegate delegate;
+  int32_t routing_id = process_host->GetNextRoutingID();
+  MockRenderWidgetHostImpl* host =
+      new MockRenderWidgetHostImpl(&delegate, process_host, routing_id);
+  RenderWidgetHostViewMac* view = new RenderWidgetHostViewMac(host, false);
+  process_host->sink().ClearMessages();
+
+  // Send a wheel event for scrolling by 3 lines.
+  // Verifies that SourceEventType exists in forwarded LatencyInfo object.
+  NSEvent* wheelEvent = MockScrollWheelEventWithPhase(@selector(phaseBegan), 3);
+  [view->cocoa_view() scrollWheel:wheelEvent];
+  ASSERT_TRUE(host->lastWheelEventLatencyInfo.source_event_type() ==
+              ui::SourceEventType::WHEEL);
+
+  // Clean up.
+  host->ShutdownAndDestroyWidget(true);
+}
+
 TEST_F(RenderWidgetHostViewMacTest, ScrollWheelEndEventDelivery) {
   // Initialize the view associated with a MockRenderWidgetHostImpl, rather than
   // the MockRenderProcessHost that is set up by the test harness which mocks