Add per-fragment early-out for getCharNumAtPosition

Add per-fragment early-out for getCharNumAtPosition

Since this is a spatial query, and a SVGTextFragment already contain an
approximation of it's own bounds, we can use those to perform a reasonably
efficient early-rejection test.
As an example: A TC using the textPath-data from issue 267504 [1] and a
mouse-move handler that uses getCharNumAtPosition to check which
"character" (glyph) is under the pointer consumes 0.005-0.2ms, compared to
0.2-0.5ms without this patch (before the CL in [2], this was 5-10ms!).
The TC mentioned in [2] now also weighs in at a few thousand us at worst.

[1] http://jsbin.com/imajow/1/quiet
[2] https://codereview.chromium.org/353003002

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=177230

[fs, 2014-06-27 14:16:04]

https://codereview.chromium.org/355173002/diff/1/Source/core/rendering/svg/SV...
File Source/core/rendering/svg/SVGTextQuery.cpp (right):

https://codereview.chromium.org/355173002/diff/1/Source/core/rendering/svg/SV...
Source/core/rendering/svg/SVGTextQuery.cpp:520: return
fragmentTransform.mapRect(fragmentRect);
(Pondered putting these last four lines in a method on SVGTextFragment - only
saw one additional user of this exact sequence though. Holler if you'd like me
to do that change.)

[pdr., 2014-06-30 17:57:36]

On 2014/06/27 14:16:04, fs wrote:
>
https://codereview.chromium.org/355173002/diff/1/Source/core/rendering/svg/SV...
> File Source/core/rendering/svg/SVGTextQuery.cpp (right):
> 
>
https://codereview.chromium.org/355173002/diff/1/Source/core/rendering/svg/SV...
> Source/core/rendering/svg/SVGTextQuery.cpp:520: return
> fragmentTransform.mapRect(fragmentRect);
> (Pondered putting these last four lines in a method on SVGTextFragment - only
> saw one additional user of this exact sequence though. Holler if you'd like me
> to do that change.)

LGTM

[pdr., 2014-06-30 17:57:38]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2014-06-30 17:59:11]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/fs@opera.com/355173002/1

[commit-bot: I haz the power, 2014-06-30 18:02:40]

Change committed as 177230