Reland "EDK: Move //mojo/edk/system/waitable_event* to edk/util."

Reland "EDK: Move //mojo/edk/system/waitable_event* to edk/util."

(This reverts commit dd010e1297c09b351dc82f7def154cfa63d795b1, and
relands commit c079879fb71164876098efae585c4adb37ca1315.)

We need to do some Mac-/iOS-specific things for
mojo::util::WaitableEvent (which needs to get a monotonic clock).

I haven't tested this on Mac or iOS -- it's basically cargo culted from
Chromium, with some extra modifications (to make it extra risky). I'll
try to verify that they work separately, but at least this works on
Linux and Android.

R=vardhan@google.com

Committed: https://chromium.googlesource.com/external/mojo/+/9a32daa8803a72c665cac470876f3a58262cc1ad

[vardhan, 2015-11-06 23:09:35]

lgtm

[viettrungluu, 2015-11-06 23:24:45]

Committed patchset #1 (id:1) manually as
9a32daa8803a72c665cac470876f3a58262cc1ad (presubmit successful).

[viettrungluu, 2015-11-06 23:24:59]

On 2015/11/06 23:09:35, vardhan wrote:
> lgtm

Thanks. FYI, I checked and it even works (at least on Mac).