Ignore minimum font-size for SVG text

In some circumstances, the minimum font-size would be applied to the
"scaled font", messing up rendering. Because of how the font is scaled,
this would trigger much less than one might expect.
Change the useSmartMinimumForFontSize argument to the
FontSize::getComputedSizeFromSpecifiedSize function to be about entirely
ignoring the minimum font-sizes (this function only has two callsites.)
Refactor LayoutSVGInlineText::computeNewScaledFontForStyle a bit to deal
with this new flow. Also always keep the "original" font when we compute
a scale factor of 0 - it should be invisible regardless.

BUG=232332,335725,475795,626936,664961
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2575863002
Cr-Commit-Position: refs/heads/master@{#438794}
7 files changed