Creating utility for converting TimeTicks to WebKit double and use it in the Chrome compositor.

webkit/renderer/compositor_bindings/webkit_time.cc

Index: webkit/renderer/compositor_bindings/webkit_time.cc
diff --git a/webkit/renderer/compositor_bindings/webkit_time.cc b/webkit/renderer/compositor_bindings/webkit_time.cc
new file mode 100644
index 0000000000000000000000000000000000000000..acc0a8562c2bd45ec7376f888a01d6818f9dd6c9
--- /dev/null
+++ b/webkit/renderer/compositor_bindings/webkit_time.cc
@@ -0,0 +1,53 @@
+// Copyright 2012 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 "webkit/renderer/compositor_bindings/webkit_time.h"
+
+#include <limits>
+
+#include "base/float_util.h"
+#include "base/logging.h"
+
+namespace webkit {
+
+// WebKit uses a double in seconds for representing monotonic_time.
+
+base::TimeTicks FromWebKitMonotonicTime(double monotonic_time) {
+  double d_microseconds =
+      monotonic_time * static_cast<double>(base::Time::kMicrosecondsPerSecond);
+
+  // We should never have a monotonic time value of zero
+  if (monotonic_time == 0 || d_microseconds == 0) {
+    DCHECK(false);
+    return base::TimeTicks();
+  }
+
+  DCHECK(!base::IsNaN(d_microseconds));
+  DCHECK(base::IsFinite(d_microseconds));
+
+  DCHECK(d_microseconds >=
+             static_cast<double>(std::numeric_limits<int64>::min()) &&
+         d_microseconds <=
+             static_cast<double>(std::numeric_limits<int64>::max()));
+
+  return base::TimeTicks::FromInternalValue(static_cast<int64>(d_microseconds));
+}
+
+// A double only has 53 bits of precision and can not represent the full range
+// of an int64 used in base::TimeTicks
+double ToWebKitMonotonicTime(base::TimeTicks monotonic_time) {
+  // We should never be sending a null TimeTicks to WebKit
+  if (monotonic_time.is_null()) {
+    DCHECK(false);
+    return 0;
+  }
+
+  int64 ticks = monotonic_time.ToInternalValue();
+  DCHECK(ticks >= -powf(2, 53) && ticks <= powf(2, 53));
+
+  return (static_cast<double>(ticks) /
+          static_cast<double>(base::Time::kMicrosecondsPerSecond));
+}
+
+}  // namespace webkit