[Extensions UI] Tweak the constants for extension action grayscaling

[Extensions UI] Tweak the constants for extension action grayscaling

The previous grayscaling wasn't enough for extension actions that were mostly
black-and-white. Make it a little more noticable. Note that this is still a
problem for extension actions that just happen to be gray by default as well
as for a11y. :( See crbug.com/597657.

BUG=597981
Review URL: https://codereview.chromium.org/1834293003

Cr-Commit-Position: refs/heads/master@{#383578}
(cherry picked from commit f51a8dcc39fba8b6ce644a54f1ff3814e255b03e)

Committed: https://chromium.googlesource.com/chromium/src/+/78165fb9893e4064ba964eaf1a1691f48cda31eb

[Devlin, 2016-03-30 22:29:40]

Description was changed from

==========
[Extensions UI] Tweak the constants for extension action grayscaling

The previous grayscaling wasn't enough for extension actions that were mostly
black-and-white. Make it a little more noticable. Note that this is still a
problem for extension actions that just happen to be gray by default as well
as for a11y. :( See crbug.com/597657.

BUG=597981

Review URL: https://codereview.chromium.org/1834293003

Cr-Commit-Position: refs/heads/master@{#383578}
(cherry picked from commit f51a8dcc39fba8b6ce644a54f1ff3814e255b03e)
==========

to

==========
[Extensions UI] Tweak the constants for extension action grayscaling

The previous grayscaling wasn't enough for extension actions that were mostly
black-and-white. Make it a little more noticable. Note that this is still a
problem for extension actions that just happen to be gray by default as well
as for a11y. :( See crbug.com/597657.

BUG=597981

Review URL: https://codereview.chromium.org/1834293003

Cr-Commit-Position: refs/heads/master@{#383578}
(cherry picked from commit f51a8dcc39fba8b6ce644a54f1ff3814e255b03e)

Committed:
https://chromium.googlesource.com/chromium/src/+/78165fb9893e4064ba964eaf1a16...
==========

[Devlin, 2016-03-30 22:29:41]

Committed patchset #1 (id:1) manually as
78165fb9893e4064ba964eaf1a1691f48cda31eb.