Motown: Use new TimelineTransform and related definitions

mojo/services/media/common/cpp/timeline.h

+// Copyright 2016 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.
+
+#ifndef MOJO_SERVICES_MEDIA_COMMON_CPP_TIMELINE_H_
+#define MOJO_SERVICES_MEDIA_COMMON_CPP_TIMELINE_H_
+
+#include <stdint.h>
+#include <chrono>  // NOLINT(build/c++11)
+
+// TODO(johngro): As we add support for other environments, extend this list.
+#if defined(OS_POSIX)
+#include "mojo/services/media/common/cpp/platform/posix/local_time.h"
+#else
+// TODO(johngro): consider adding a #warning or #info to inform the user that
+// they are using the generic implementation of LocalTime, and really should get
+// around to implementing proper platform support ASAP.
+#include "mojo/services/media/common/cpp/platform/generic/local_time.h"
+#endif
+
+namespace mojo {
+namespace media {
+
+// Some helpful constants and static methods relating to timelines.
+class Timeline {
+ public:
+  // Returns the current local time in nanoseconds since epoch.
+  static int64_t local_now() {
+    return local_time::Clock::now().time_since_epoch().count();
+  }
+
+  template <typename T>
+  static constexpr int64_t ns_from_seconds(T seconds) {
+    return static_cast<int64_t>(seconds * std::nano::den);

[kulakowski, 2016/05/24 13:57:24]

Elsewhere, in code either you or John wrote (I'm sorry I can't find it again in
the ~40 files in the CL), was a comment about std::ratio being verboten,
presumably per the style guide. Did that change? It'd be nice, I think this is a
nice way to canonically give this value without having to count 0s.

[dalesat, 2016/05/24 18:09:15]

Yes, I remember that, too, but I can't find it. I felt OK about using these
here, because John used them in local_time.h, a file with similar scope of
concerns. I can certainly change this, but I frankly don't see the harm in using
these definitions.

+  }
+
+  template <typename T>
+  static constexpr int64_t ns_from_ms(T milliseconds) {
+    return static_cast<int64_t>(milliseconds *
+                                (std::nano::den / std::milli::den));
+  }
+
+  template <typename T>
+  static constexpr int64_t ns_from_us(T microseconds) {
+    return static_cast<int64_t>(microseconds *
+                                (std::nano::den / std::micro::den));
+  }
+};
+
+}  // namespace media
+}  // namespace mojo
+
+#endif  // MOJO_SERVICES_MEDIA_COMMON_CPP_TIMELINE_H_