Properly recompute SVG font size under zoom

Source/core/rendering/svg/RenderSVGInlineText.cpp

 /*
  * Copyright (C) 2006 Oliver Hunt <ojh16@student.canterbury.ac.nz>
  * Copyright (C) 2006 Apple Computer Inc.
  * Copyright (C) 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2008 Rob Buis <buis@kde.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 202 matching lines @@
     computeNewScaledFontForStyle(this, style(), m_scalingFactor, m_scaledFont);
 }
 
 void RenderSVGInlineText::computeNewScaledFontForStyle(RenderObject* renderer, const RenderStyle* style, float& scalingFactor, Font& scaledFont)
 {
     ASSERT(style);
     ASSERT(renderer);
 
     // Alter font-size to the right on-screen value to avoid scaling the glyphs themselves, except when GeometricPrecision is specified.
     scalingFactor = SVGRenderingContext::calculateScreenFontSizeScalingFactor(renderer);
-    if (scalingFactor == 1 || !scalingFactor) {

[f(malita), 2014/08/27 12:44:31]

Not related to this CL, but do you know why we reset 0.0 -> 1.0? It seems odd
that at the low end of our range, the font snaps back to visible.

[pdr., 2014/08/27 18:09:51]

I agree, this is weird.

I tried converting this to an assert:
    ASSERT(scalingFactor);
    if (style->effectiveZoom() == 1 && scalingFactor == 1)

Unfortunately it looks like scalingFactor will sometimes actually be zero. This
is probably a bug since scalingFactor is effectively the full ctm. This code has
some gross bugs and does not work properly with the compositing update :/

+    if (style->effectiveZoom() == 1 && (scalingFactor == 1 || !scalingFactor)) {
         scalingFactor = 1;
         scaledFont = style->font();
         return;
     }
 
     if (style->fontDescription().textRendering() == GeometricPrecision)
         scalingFactor = 1;
 
     FontDescription fontDescription(style->fontDescription());
 
     Document& document = renderer->document();
     // FIXME: We need to better handle the case when we compute very small fonts below (below 1pt).
     fontDescription.setComputedSize(FontSize::getComputedSizeFromSpecifiedSize(&document, scalingFactor, fontDescription.isAbsoluteSize(), fontDescription.specifiedSize(), DoNotUseSmartMinimumForFontSize));
 
     scaledFont = Font(fontDescription);
     scaledFont.update(document.styleEngine()->fontSelector());
 }
 
 }