Bug 1430173 - Reduce the precision of all explicit clocks to 2ms. r=baku, a=RyanVM

Backport to ESR where we don't have the ResistFingerprinting component.

MozReview-Commit-ID: 9bjycHjR3SF

--HG--
extra : transplant_source : %EA%03%21%0A%E9%3F%8E%CD%7C%D79f%96%85%96%00%5D%7F%95X

1 files changed, 35 insertions, 0 deletions

diff --git a/dom/base/TimerClamping.cpp b/dom/base/TimerClamping.cpp
new file mode 100755
index 000000000..70639686b
--- /dev/null
+++ b/dom/base/TimerClamping.cpp
@@ -0,0 +1,35 @@
+/* -*- 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 "TimerClamping.h"
+
+namespace mozilla {
+
+/* static */
+double
+TimerClamping::ReduceSTimeValue(double aTime)
+{
+  static const double maxResolutionS = .002;
+  return floor(aTime / maxResolutionS) * maxResolutionS;
+}
+
+/* static */
+double
+TimerClamping::ReduceMsTimeValue(double aTime)
+{
+  static const double maxResolutionMs = 2;
+  return floor(aTime / maxResolutionMs) * maxResolutionMs;
+}
+
+/* static */
+double
+TimerClamping::ReduceUsTimeValue(double aTime)
+{
+  static const double maxResolutionUs = 2000;
+  return floor(aTime / maxResolutionUs) * maxResolutionUs;
+}
+
+}
\ No newline at end of file