[PE] Fix text selection of <svg:text> subject to 'textLength'

With 'textLength' and 'lengthAdjust' with the value 'spacingAndGlyphs',
each SVGTextFragment is subject to an additional scale factor that
stretches the glyphs along the x- or y-axis.
This scale factor was not (any longer) taken into account by
SVGInlineTextBox::OffsetForPositionInFragment, which resulted in the
incorrect offset being calculcated.
Apply the (inverse) length_adjust_scale from SVGTextFragment before
querying the font for an offset.

Remove the |include_partial_glyphs| argument from
SVGInlineTextBox::OffsetForPositionInFragment since it's always true,
and also use 'float' rather LayoutUnit for the position.
Remove the dead |horizontal_glyph_stretch_| member variable from TextRun
since it's no longer used (since the simple shaper path was removed.)

Bug: 793075
Change-Id: Ia7d369d914f5afd87d198b7b21077e180fc8bc59
Reviewed-on: https://chromium-review.googlesource.com/824162
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523787}
48 files changed