Insert TRACE_EVENT macros for the sampling profiler into not performance-sensitive places

- Implement TraceEvent::SamplingState0Scope.

- Insert TraceEvent::SamplingState0Scope into where performance is not sensitive.
I'll insert the macros to performance-sensitive places in a follow-up CL.

- Replace "TraceEventAPIAtomicWord" with "long", since it's implemented as long
in the Chromium side. "TraceEventAPIAtomicWord" is confusing since it gives
us an impression that it's already implemented as a thread-safe and atomic word.

R=abarth@chromium.org
BUG=241743

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=152694

Review URL: https://codereview.chromium.org/17377006

git-svn-id: svn://svn.chromium.org/blink/trunk@152741 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix a zooming bug with EM MQs

BUG=245449

EM MQs were using calculated font size (which include the zooming factor) in order to translate the expected MQ size to CSS pixels.
At the same time, adjustForAbsoluteZoom was taking the zoom into account to decrease the number of CSS pixels that fit into the viewport.
That created a situation where the zoom is taken into account twice, causing a difference between EM MQs and PX MQs.
That wasn't as bad as it could be because the calculated font size wasn't updating itself on every zoom step, but there was still visible difference.

This change simply turns off font calculation for the CSS pixel computation, which results in parity between PX and EM MQs.

I also added a layout test that covers this issue.

Review URL: https://chromiumcodereview.appspot.com/15841015

git-svn-id: svn://svn.chromium.org/blink/trunk@152742 bbb929c8-8fbe-4397-9dbb-9b2b20218538