Initiate webfont download right after style recalc

Currently WebFont download is queued during layout, and actual download is
delayed until after layout. This patch makes CSSFontFace::willUseFontData()
enqueue font download, which is called in style calc time. StyleResolver
kicks off font downloads, along with other pending resources.

UMA metrics (WebFont.Resource.StyleRecalcToDownloadLatency) shows
this reduces webfont download latency 114ms at the 50 percentile.
This patch also removes FontResource::FontResourceHistograms as we
collected sufficient data.

BUG=246492
TEST=Covered by existing tests

Review URL: https://codereview.chromium.org/63713002

git-svn-id: svn://svn.chromium.org/blink/trunk@162179 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[Refactoring] Remove include "core/inspector/InspectorInstrumentation.h" from SelectorChecker.h

To make it possible to add include "StyleResolver.h" to StyleEngine.h,
We need to remove the above include from SelectorChecker.h.

BUG=305885
TEST=No layout tests, just refactoring.

Review URL: https://codereview.chromium.org/70063005

git-svn-id: svn://svn.chromium.org/blink/trunk@162180 bbb929c8-8fbe-4397-9dbb-9b2b20218538