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

5 files changed, 63 insertions, 3 deletions

diff --git a/dom/base/File.cpp b/dom/base/File.cpp
index 46b37b976..8602a3064 100644..100755
--- a/dom/base/File.cpp
+++ b/dom/base/File.cpp
@@ -29,6 +29,7 @@
 #include "nsStringStream.h"
 #include "nsJSUtils.h"
 #include "nsPrintfCString.h"
+#include "mozilla/TimerClamping.h"
 #include "mozilla/SHA1.h"
 #include "mozilla/CheckedInt.h"
 #include "mozilla/Preferences.h"
@@ -727,7 +728,7 @@ BlobImplBase::GetLastModified(ErrorResult& aRv)
     mLastModificationDate = PR_Now();
   }
 
-  return mLastModificationDate / PR_USEC_PER_MSEC;
+  return TimerClamping::ReduceUsTimeValue(mLastModificationDate) / PR_USEC_PER_MSEC;
 }
 
 void
diff --git a/dom/base/MultipartBlobImpl.cpp b/dom/base/MultipartBlobImpl.cpp
index ba26d07f9..03bb62add 100644..100755
--- a/dom/base/MultipartBlobImpl.cpp
+++ b/dom/base/MultipartBlobImpl.cpp
@@ -17,6 +17,7 @@
 #include "nsContentUtils.h"
 #include "nsIScriptError.h"
 #include "nsIXPConnect.h"
+#include "mozilla/TimerClamping.h"
 #include <algorithm>
 
 using namespace mozilla;
@@ -270,8 +271,7 @@ MultipartBlobImpl::SetLengthAndModifiedDate(ErrorResult& aRv)
     //   var x = new Date(); var f = new File(...);
     //   x.getTime() < f.dateModified.getTime()
     // could fail.
-    mLastModificationDate =
-      lastModifiedSet ? lastModified * PR_USEC_PER_MSEC : JS_Now();
+    mLastModificationDate = TimerClamping::ReduceUsTimeValue(lastModifiedSet ? lastModified * PR_USEC_PER_MSEC : JS_Now());
   }
 }
 
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
diff --git a/dom/base/TimerClamping.h b/dom/base/TimerClamping.h
new file mode 100755
index 000000000..2ffd6add5
--- /dev/null
+++ b/dom/base/TimerClamping.h
@@ -0,0 +1,22 @@
+/* -*- 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/. */
+
+#ifndef TimerClamping_h___
+#define TimerClamping_h___
+
+namespace mozilla {
+
+class TimerClamping
+{
+public:
+  static double ReduceSTimeValue(double aTime);
+  static double ReduceMsTimeValue(double aTime);
+  static double ReduceUsTimeValue(double aTime);
+};
+
+}
+
+#endif /* TimerClamping_h___ */
\ No newline at end of file
diff --git a/dom/base/moz.build b/dom/base/moz.build
index 686d76e73..0fb345d22 100644..100755
--- a/dom/base/moz.build
+++ b/dom/base/moz.build
@@ -143,6 +143,7 @@ EXPORTS.mozilla += [
     'CORSMode.h',
     'FeedWriterEnabled.h',
     'TextInputProcessor.h',
+    'TimerClamping.h',
     'UseCounter.h',
 ]
 
@@ -363,6 +364,7 @@ UNIFIED_SOURCES += [
     'TextInputProcessor.cpp',
     'ThirdPartyUtil.cpp',
     'Timeout.cpp',
+    'TimerClamping.cpp',
     'TreeWalker.cpp',
     'WebKitCSSMatrix.cpp',
     'WebSocket.cpp',