Add descriptive names for different addMidpoint use cases
https://bugs.webkit.org/show_bug.cgi?id=110644

Reviewed by Ryosuke Niwa.

Midpoints are used to delineate ranges where we don't add line boxes for contents (collapsed spaces),
and to explicitly split a RenderText into multiple text runs so that text paragraph seperators get
their own line boxes. This patch encapsulates the different cases where midpoints are added to
lineMidpointState into 4 helper functions to make it clearer what's going on in each case.

No new tests. No change in functionality.

* rendering/RenderBlockLineLayout.cpp:
(WebCore::deprecatedAddMidpoint): Original function simply adds a midpoint to the lineMidpointState.
Renaming to deprecated to discourage callers.
(WebCore::startIgnoringSpaces): Adds a midpoint to start collapsing subsequent spaces. Asserts that
we have an even number of midpoints.
(WebCore::stopIgnoringSpaces): Adds the corresponding midpoint from startIgnoringSpaces and asserts
that it's an odd number.
(WebCore::ensureLineBoxInsideIgnoredSpaces): When ignoring spaces and we come across a RenderInline
that needs a line box, this function adds a pair of midpoints which ensures we'll later add a line
box for it.
(WebCore::ensureCharacterGetsLineBox): Adds a pair of midpoints in a text renderer to mark that
the current character needs its own line box. This is used by svg for absolutely positioned
characters, or for text paragraph seperators.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143812 268f45cc-cd09-0410-ab3c-d52691b4dbfc