Fix EditingStyle::mergeStyle()'s handling of custom properties

Fix EditingStyle::mergeStyle()'s handling of custom properties

This patch fixes the logic of EditingStyle::mergeStyle() to correctly
handle custom properties. Currently it serializes the CSSValue and then
reparses it, which, aside from being inefficient, doesn't work for
custom properties as the custom property name is lost (since we only
have the enum value CSSPropertyVariable).

BUG=622420
Review-Url: https://codereview.chromium.org/2103043004
Cr-Commit-Position: refs/heads/master@{#410614}
(cherry picked from commit aadb63893e4c1358d1e5139aa29552eb190682c8)

Committed: https://chromium.googlesource.com/chromium/src/+/ed9e60bc6238f29c78a85229e57a07256c4f66e4

[Timothy Loh, 2016-08-12 04:38:39]

Description was changed from

==========
Fix EditingStyle::mergeStyle()'s handling of custom properties

This patch fixes the logic of EditingStyle::mergeStyle() to correctly
handle custom properties. Currently it serializes the CSSValue and then
reparses it, which, aside from being inefficient, doesn't work for
custom properties as the custom property name is lost (since we only
have the enum value CSSPropertyVariable).

BUG=622420

Review-Url: https://codereview.chromium.org/2103043004
Cr-Commit-Position: refs/heads/master@{#410614}
(cherry picked from commit aadb63893e4c1358d1e5139aa29552eb190682c8)
==========

to

==========
Fix EditingStyle::mergeStyle()'s handling of custom properties

This patch fixes the logic of EditingStyle::mergeStyle() to correctly
handle custom properties. Currently it serializes the CSSValue and then
reparses it, which, aside from being inefficient, doesn't work for
custom properties as the custom property name is lost (since we only
have the enum value CSSPropertyVariable).

BUG=622420

Review-Url: https://codereview.chromium.org/2103043004
Cr-Commit-Position: refs/heads/master@{#410614}
(cherry picked from commit aadb63893e4c1358d1e5139aa29552eb190682c8)

Committed:
https://chromium.googlesource.com/chromium/src/+/ed9e60bc6238f29c78a85229e57a...
==========

[Timothy Loh, 2016-08-12 04:38:43]

Committed patchset #1 (id:1) manually as
ed9e60bc6238f29c78a85229e57a07256c4f66e4.