UMA histograms to measure whether / how long blank text is rendered for loading web fonts

UMA histograms to measure whether / how long blank text is rendered for loading web fonts

This patch adds two UMA metrics:

WebFont.BlankTextShownTime histogram tracks the time we spent showing
blank text. This measures the time between when the "loading fallback"
font is drawn for the first time, and when FontData for the downloaded
web font is created.

WebFont.HadBlankText is recorded once per page load if the page uses
any web fonts. The value is 1 if we ended up showing blank text at
least once, 0 otherwise.

BUG=345839
TEST=Manually tested with chrome://histograms

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168541

[dglazkov, 2014-03-04 17:24:08]

lgtm

https://codereview.chromium.org/180273020/diff/1/Source/core/css/CSSFontFaceS...
File Source/core/css/CSSFontFaceSource.cpp (right):

https://codereview.chromium.org/180273020/diff/1/Source/core/css/CSSFontFaceS...
Source/core/css/CSSFontFaceSource.cpp:306: if (m_fallbackPaintTime > 0) {
Early return?

[Kunihiko Sakamoto, 2014-03-05 08:55:59]

https://codereview.chromium.org/180273020/diff/1/Source/core/css/CSSFontFaceS...
File Source/core/css/CSSFontFaceSource.cpp (right):

https://codereview.chromium.org/180273020/diff/1/Source/core/css/CSSFontFaceS...
Source/core/css/CSSFontFaceSource.cpp:306: if (m_fallbackPaintTime > 0) {
On 2014/03/04 17:24:08, Dimitri Glazkov wrote:
> Early return?

Done.

[Kunihiko Sakamoto, 2014-03-05 08:56:08]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2014-03-05 08:57:17]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ksakamoto@chromium.org/180273020/20001

[commit-bot: I haz the power, 2014-03-05 20:57:27]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ksakamoto@chromium.org/180273020/20001

[commit-bot: I haz the power, 2014-03-05 22:19:55]

Change committed as 168541