1 files changed, 74 insertions, 0 deletions
diff --git a/gfx/layers/apz/src/PotentialCheckerboardDurationTracker.cpp b/gfx/layers/apz/src/PotentialCheckerboardDurationTracker.cpp
new file mode 100644
index 0000000000..f3d5538ba0
--- /dev/null
+++ b/gfx/layers/apz/src/PotentialCheckerboardDurationTracker.cpp
@@ -0,0 +1,74 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "PotentialCheckerboardDurationTracker.h"
+
+#include "mozilla/Telemetry.h"  // for Telemetry
+
+namespace mozilla {
+namespace layers {
+
+PotentialCheckerboardDurationTracker::PotentialCheckerboardDurationTracker()
+    : mInCheckerboard(false), mInTransform(false) {}
+
+void PotentialCheckerboardDurationTracker::CheckerboardSeen() {
+  // This might get called while mInCheckerboard is already true
+  if (!Tracking()) {
+    mCurrentPeriodStart = TimeStamp::Now();
+  }
+  mInCheckerboard = true;
+}
+
+void PotentialCheckerboardDurationTracker::CheckerboardDone(
+    bool aRecordTelemetry) {
+  MOZ_ASSERT(Tracking());
+  mInCheckerboard = false;
+  if (!Tracking()) {
+    if (aRecordTelemetry) {
+      mozilla::Telemetry::AccumulateTimeDelta(
+          mozilla::Telemetry::CHECKERBOARD_POTENTIAL_DURATION,
+          mCurrentPeriodStart);
+    }
+  }
+}
+
+void PotentialCheckerboardDurationTracker::InTransform(bool aInTransform,
+                                                       bool aRecordTelemetry) {
+  if (aInTransform == mInTransform) {
+    // no-op
+    return;
+  }
+
+  if (!Tracking()) {
+    // Because !Tracking(), mInTransform must be false, and so aInTransform
+    // must be true (or we would have early-exited this function already).
+    // Therefore, we are starting a potential checkerboard period.
+    mInTransform = aInTransform;
+    mCurrentPeriodStart = TimeStamp::Now();
+    return;
+  }
+
+  mInTransform = aInTransform;
+
+  if (!Tracking()) {
+    // Tracking() must have been true at the start of this function, or we
+    // would have taken the other !Tracking branch above. If it's false now,
+    // it means we just stopped tracking, so we are ending a potential
+    // checkerboard period.
+    if (aRecordTelemetry) {
+      mozilla::Telemetry::AccumulateTimeDelta(
+          mozilla::Telemetry::CHECKERBOARD_POTENTIAL_DURATION,
+          mCurrentPeriodStart);
+    }
+  }
+}
+
+bool PotentialCheckerboardDurationTracker::Tracking() const {
+  return mInTransform || mInCheckerboard;
+}
+
+}  // namespace layers
+}  // namespace mozilla