Multi-hop reference cycles not detected.

Multi-hop reference cycles not detected.
https://bugs.webkit.org/show_bug.cgi?id=149181

Reviewed by John Honeycutt.

Source/WebCore:

SVG's cycle detection was not picking up a
case where an element was drawing a pattern, that
referenced another pattern, that referenced another
pattern, that referenced the original pattern.

The issue was that we were forgetting to check the
children of the renderer itself, rather than just
the children of the referenced renderers.

Found by running a test from Blink.

I also took the opportunity to clean up the debugging
code that logs cycle detection.

Test: svg/custom/pattern-3-step-cycle.html

* platform/Logging.h: Add a new SVG channel. I can't believe we
didn't already have one!
* rendering/svg/SVGResourcesCycleSolver.cpp:
(WebCore::SVGResourcesCycleSolver::resourceContainsCycles): Check the referenced
resources for cycles.
(WebCore::SVGResourcesCycleSolver::resolveCycles): Logging update.

LayoutTests:

Test comes from:
https://chromium.googlesource.com/chromium/blink/+/master/LayoutTests/svg/custom/pattern-3-step-cycle.html

* svg/custom/pattern-3-step-cycle-expected.txt: Added.
* svg/custom/pattern-3-step-cycle.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@189954 268f45cc-cd09-0410-ab3c-d52691b4dbfc