Use swap-promise to improve first* paint times

content/renderer/gpu/render_widget_compositor.cc

 // Copyright (c) 2013 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/renderer/gpu/render_widget_compositor.h"
 
 #include <stddef.h>
 
 #include <cmath>
 #include <limits>
@@ skipping 168 matching lines @@
 static_assert(int(blink::kWebBrowserControlsHidden) == int(cc::HIDDEN),
               "mismatching enums: HIDDEN");
 static_assert(int(blink::kWebBrowserControlsShown) == int(cc::SHOWN),
               "mismatching enums: SHOWN");
 
 static cc::BrowserControlsState ConvertBrowserControlsState(
     WebBrowserControlsState state) {
   return static_cast<cc::BrowserControlsState>(state);
 }
 
+double MonotonicallyIncreasingTime() {
+  return base::TimeTicks::Now().ToInternalValue() /
+         static_cast<double>(base::Time::kMicrosecondsPerSecond);

[sunnyps, 2017/05/02 01:20:46]

nit: can you put the static_case<double> on the first part of the expression
(...ToInternalValue)?

[panicker, 2017/05/02 21:21:36]

Done.

+}
+
 }  // namespace
 
+RenderWidgetCompositor::ReportTimeSwapPromise::ReportTimeSwapPromise(
+    ReportTimeCallback callback,
+    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner)
+    : callback_(callback), task_runner_(task_runner) {}
+
+RenderWidgetCompositor::ReportTimeSwapPromise::~ReportTimeSwapPromise() {}
+
+void RenderWidgetCompositor::ReportTimeSwapPromise::DidSwap() {
+  task_runner_->PostTask(
+      FROM_HERE,
+      base::BindOnce(callback_, true, MonotonicallyIncreasingTime()));
+}
+
+cc::SwapPromise::DidNotSwapAction
+RenderWidgetCompositor::ReportTimeSwapPromise::DidNotSwap(
+    cc::SwapPromise::DidNotSwapReason reason) {
+  task_runner_->PostTask(FROM_HERE, base::BindOnce(callback_, false, 0));
+  return cc::SwapPromise::DidNotSwapAction::BREAK_PROMISE;
+}
+
+int64_t RenderWidgetCompositor::ReportTimeSwapPromise::TraceId() const {
+  return 0;
+}
+
 // static
 std::unique_ptr<RenderWidgetCompositor> RenderWidgetCompositor::Create(
     RenderWidgetCompositorDelegate* delegate,
     CompositorDependencies* compositor_deps) {
   std::unique_ptr<RenderWidgetCompositor> compositor(
       new RenderWidgetCompositor(delegate, compositor_deps));
   return compositor;
 }
 
 RenderWidgetCompositor::RenderWidgetCompositor(
@@ skipping 947 matching lines @@
 
 void RenderWidgetCompositor::SetContentSourceId(uint32_t id) {
   layer_tree_host_->SetContentSourceId(id);
 }
 
 void RenderWidgetCompositor::SetLocalSurfaceId(
     const cc::LocalSurfaceId& local_surface_id) {
   layer_tree_host_->SetLocalSurfaceId(local_surface_id);
 }
 
+void RenderWidgetCompositor::NotifySwapTime(
+    base::Callback<void(bool, double)> callback) {
+  QueueSwapPromise(base::MakeUnique<ReportTimeSwapPromise>(
+      std::move(callback), base::ThreadTaskRunnerHandle::Get()));
+}
+
 }  // namespace content