Cheat to go fast, but be careful in debug mode.

Cheat to go fast, but be careful in debug mode.

Turns out recording actual text metrics is currently really slow.
If we want to compete with the (cheating) status quo, gotta cheat too.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/a19afb418027800c245ad19d651d8cf2071c9d70

[mtklein, 2014-08-19 22:52:08]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-08-19 22:52:43]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/mtklein@chromium.org/494483002/1

[commit-bot: I haz the power, 2014-08-19 22:52:43]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from a valid reviewer till 2014-08-20 04:52 UTC

[reed1, 2014-08-20 00:45:55]

lgtm

[commit-bot: I haz the power, 2014-08-20 00:47:20]

Committed patchset #1 (1) as a19afb418027800c245ad19d651d8cf2071c9d70

[robertphillips, 2014-08-20 13:04:21]

Do we have any idea why getFontMetrics is so slow (I thought we were caching the
answers so the expensive parts would be amortized away)?

[reed1, 2014-08-20 13:34:01]

On 2014/08/20 13:04:21, robertphillips wrote:
> Do we have any idea why getFontMetrics is so slow (I thought we were caching
the
> answers so the expensive parts would be amortized away)?

It is slow because we have to get into the font cache (via a mutex), find the
right entry, and get out.