https://bugs.webkit.org/show_bug.cgi?id=123827

Reviewed by Ryosuke Niwa.

Source/WebCore:

Add compile-time guard, ENABLE(TEXT_SELECTION), to enable or
disable selection painting in WebCore (enabled by default).

On iOS we disable WebCore selection painting and have UIKit
paint the selection.

* rendering/InlineTextBox.cpp:
(WebCore::InlineTextBox::paintSelection): Only paint selection when
TEXT_SELECTION is enabled.
* rendering/LogicalSelectionOffsetCaches.h:
(WebCore::LogicalSelectionOffsetCaches::LogicalSelectionOffsetCaches):
For now, add a ENABLE(TEXT_SELECTION)-guard around an assertion. Added
a FIXME comment to investigate the callers and either move the assertion
to the appropriate callers or structure the code such that we can remove
the assertion.
* rendering/RenderBlock.cpp:
(WebCore::RenderBlock::paintSelection): Only paint selection when
TEXT_SELECTION is enabled.
* rendering/TextPaintStyle.cpp:
(WebCore::computeTextSelectionPaintStyle): Only compute the selection
paint style when TEXT_SELECTION is enabled. Otherwise, return a paint
style identical to the text paint style. Also, substitute nullptr for 0.

Source/WTF:

Enable selection painting by default on all ports except iOS.

* wtf/FeatureDefines.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@158750 268f45cc-cd09-0410-ab3c-d52691b4dbfc