Let only the root layer paint root background

Let only the root layer paint root background

When the viewport has fixed background, we may create a dedicated
GraphicsLayer (CompositedLayerMapping::m_backgroundLayer) for the
root background. Previously we used PaintLayerPaintingRootBackgroundOnly
and PaintLayerPaintingCompositingForegroundPhase flags when painting
the layer. The second flag was necessary before we refactored viewport
background painting into ViewPainter, because we needed the layout
objects of the document element or the body element to paint the
viewport background.

Now we need only the root layer to paint root background.

BUG=595839
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Committed: https://crrev.com/f218841e39d1cb7bad5a0711081e75042bca316e
Cr-Commit-Position: refs/heads/master@{#415694}

[Xianzhu, 2016-08-31 15:58:24]

Description was changed from

==========
Let only the root layer paint root background

When the viewport has fixed background, we may create a dedicated
GraphicsLayer (CompositedLayerMapping::m_backgroundLayer) for the
root background. Previously we used PaintLayerPaintingRootBackgroundOnly
and PaintLayerPaintingCompositingForegroundPhase flags when painting
the layer. The second flag was necessary before we refactored viewport
background painting into ViewPainter, because we needed the layout
objects of the document element or the body element to paint the
viewport background.

Now we need only the root layer to paint root background.

BUG=595839
==========

to

==========
Let only the root layer paint root background

When the viewport has fixed background, we may create a dedicated
GraphicsLayer (CompositedLayerMapping::m_backgroundLayer) for the
root background. Previously we used PaintLayerPaintingRootBackgroundOnly
and PaintLayerPaintingCompositingForegroundPhase flags when painting
the layer. The second flag was necessary before we refactored viewport
background painting into ViewPainter, because we needed the layout
objects of the document element or the body element to paint the
viewport background.

Now we need only the root layer to paint root background.

BUG=595839
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[Xianzhu, 2016-08-31 15:58:26]

The CQ bit was checked by wangxianzhu@chromium.org to run a CQ dry run

[Xianzhu, 2016-08-31 15:58:42]

wangxianzhu@chromium.org changed reviewers:
+ chrishtr@chromium.org

[commit-bot: I haz the power, 2016-08-31 15:58:43]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Xianzhu, 2016-08-31 16:01:57]

The CQ bit was checked by wangxianzhu@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-08-31 16:02:15]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Xianzhu, 2016-08-31 16:10:54]

The CQ bit was checked by wangxianzhu@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-08-31 16:11:09]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-31 17:55:11]

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

[commit-bot: I haz the power, 2016-08-31 17:55:12]

Dry run: This issue passed the CQ dry run.

[chrishtr, 2016-08-31 18:34:50]

The CQ bit was checked by chrishtr@chromium.org

[chrishtr, 2016-08-31 18:34:51]

lgtm

[commit-bot: I haz the power, 2016-08-31 18:35:20]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-31 18:39:23]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-08-31 18:42:19]

Description was changed from

==========
Let only the root layer paint root background

When the viewport has fixed background, we may create a dedicated
GraphicsLayer (CompositedLayerMapping::m_backgroundLayer) for the
root background. Previously we used PaintLayerPaintingRootBackgroundOnly
and PaintLayerPaintingCompositingForegroundPhase flags when painting
the layer. The second flag was necessary before we refactored viewport
background painting into ViewPainter, because we needed the layout
objects of the document element or the body element to paint the
viewport background.

Now we need only the root layer to paint root background.

BUG=595839
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Let only the root layer paint root background

When the viewport has fixed background, we may create a dedicated
GraphicsLayer (CompositedLayerMapping::m_backgroundLayer) for the
root background. Previously we used PaintLayerPaintingRootBackgroundOnly
and PaintLayerPaintingCompositingForegroundPhase flags when painting
the layer. The second flag was necessary before we refactored viewport
background painting into ViewPainter, because we needed the layout
objects of the document element or the body element to paint the
viewport background.

Now we need only the root layer to paint root background.

BUG=595839
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Committed: https://crrev.com/f218841e39d1cb7bad5a0711081e75042bca316e
Cr-Commit-Position: refs/heads/master@{#415694}
==========

[commit-bot: I haz the power, 2016-08-31 18:42:19]

Patchset 2 (id:??) landed as
https://crrev.com/f218841e39d1cb7bad5a0711081e75042bca316e
Cr-Commit-Position: refs/heads/master@{#415694}