Deflake tests using ahem font with @font-face.

Deflake tests using ahem font with @font-face.

Instead of trying to fix the issues about sideloaded font on Windows
and similar issue on Mac, we use @font-face instead, and force a layout
during DOMContentLoad to ensure the ahem font is loaded before onload
fires and test finishes.

This CL converts the tests using ahem font and marked flaky in
TestExpectations and FlakyTests.

Other benefits of this CL are:
- No more need of platform-specific methods to register the 'Ahem' font
  family;
- We can run the tests directly in browser and browser-mode content_shell
  without requiring 'Ahem' font registered in the system.

Next steps:
- Convert all tests using ahem font to this style;
- Ensure all tests using @font-face to force a layout before onload;
- Convert all tests using pre-registered fonts to this style;
- Write a presubmit rule to ensure the above;
- Remove the platform-specific code for pre-registering fonts.

BUG=392046
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197873

[Xianzhu, 2015-06-25 16:11:43]

wangxianzhu@chromium.org changed reviewers:
+ dpranke@google.com, ksakamoto@chromium.org, pdr@chromium.org

[Xianzhu, 2015-06-25 16:44:44]

Patchset #5 (id:80001) has been deleted

[Kunihiko Sakamoto, 2015-06-26 01:04:24]

lgtm

[Xianzhu, 2015-06-26 01:45:34]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2015-06-26 01:46:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1204023002/140001

[commit-bot: I haz the power, 2015-06-26 01:52:41]

Committed patchset #7 (id:140001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197873