[Reland] Invalidate whitespace text on text color changes

[Reland] Invalidate whitespace text on text color changes

This patch updates the optimization added in [1] to invalidate
whitespace text on color changes because whitespace text can have
decorations such as underlines which still need to repaint.

The big idea of the optimization in [1] is to not unnecessarily repaint
expensive items such as images that are in an <a> element. On hover, <a>
will change color and underline styles which should not affect images.
This patch adds a test to prove this optimization still works and
prevents it from breaking in the future.

This patch contains a fix for a performance regression[2] where text
nodes without text (i.e., !firstTextBox) would be invalidated. This is
tested by fast/repaint/inline-outline-repaint-2.html but was incorrectly
thought to be a benign change in the original patch. Additional comments
have been added both about the optimization and about the tricky
empty-text case. Additionally, hasTextBoxes has been introduced to make
this area cleaner.

[1] https://src.chromium.org/viewvc/blink?view=rev&revision=152046
[2] https://src.chromium.org/viewvc/blink?view=rev&revision=202374

TBR=chrishtr
BUG=529944
Committed: https://crrev.com/72f85dacbbef4c117efdb8e353036873d167b989
Cr-Commit-Position: refs/heads/master@{#350412}

[pdr., 2015-09-23 18:46:40]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2015-09-23 18:49:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1363913004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1363913004/1

[commit-bot: I haz the power, 2015-09-23 20:07:22]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-23 20:07:23]

Try jobs failed on following builders:
  win_chromium_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[pdr., 2015-09-23 20:08:14]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2015-09-23 20:10:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1363913004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1363913004/1

[commit-bot: I haz the power, 2015-09-23 20:22:41]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-23 20:22:42]

Try jobs failed on following builders:
  linux_chromium_asan_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[pdr., 2015-09-23 21:05:40]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2015-09-23 21:06:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1363913004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1363913004/1

[commit-bot: I haz the power, 2015-09-23 21:23:53]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-23 21:23:54]

Try jobs failed on following builders:
  linux_chromium_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[pdr., 2015-09-23 22:10:25]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2015-09-23 22:11:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1363913004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1363913004/1

[commit-bot: I haz the power, 2015-09-24 00:21:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-24 00:35:20]

Patchset 1 (id:??) landed as
https://crrev.com/72f85dacbbef4c117efdb8e353036873d167b989
Cr-Commit-Position: refs/heads/master@{#350412}

[pdr., 2015-09-24 04:20:41]

On 2015/09/24 at 00:35:20, commit-bot wrote:
> Patchset 1 (id:??) landed as
https://crrev.com/72f85dacbbef4c117efdb8e353036873d167b989
> Cr-Commit-Position: refs/heads/master@{#350412}

Original review (pre-blink-merge) was at
https://codereview.chromium.org/1363823002.