DevTools: simplify & fix property overload logic

DevTools: simplify & fix property overload logic

- Simplify StyleSectionModel.isPropertyOverloaded method. It does not
  require a second parameter any more.
- As a side effect of previous bullet, fix a bug and add a test.
- Centralize all logic of computing used properties in a single place.

BUG=496263
R=pfeldman

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201190

[lushnikov, 2015-08-26 00:00:26]

ptal

[pfeldman, 2015-08-26 01:32:38]

lgtm

https://codereview.chromium.org/1320543002/diff/1/Source/devtools/front_end/e...
File Source/devtools/front_end/elements/StylesSectionModel.js (right):

https://codereview.chromium.org/1320543002/diff/1/Source/devtools/front_end/e...
Source/devtools/front_end/elements/StylesSectionModel.js:340: for (var property
of style.leadingProperties()) {
I think we should stop doing this and implement it on the backend. Otherwise,
these are just the parts of the logic that won't be needed.

[lushnikov, 2015-08-26 01:35:44]

https://codereview.chromium.org/1320543002/diff/1/Source/devtools/front_end/e...
File Source/devtools/front_end/elements/StylesSectionModel.js (right):

https://codereview.chromium.org/1320543002/diff/1/Source/devtools/front_end/e...
Source/devtools/front_end/elements/StylesSectionModel.js:340: for (var property
of style.leadingProperties()) {
We will still have leadingProperties when your changes are implemented.
Anyway, this is the last piece which was blocking the revert of CSSP

[lushnikov, 2015-08-26 01:35:48]

The CQ bit was checked by lushnikov@chromium.org

[commit-bot: I haz the power, 2015-08-26 01:36:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1320543002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1320543002/1

[commit-bot: I haz the power, 2015-08-26 03:04:07]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201190