Make SVG*StringList and SVGStringListTearOff scarcer

(Primarily) because of their inclusion in the SVGTests interface, these
two make their way into a lot more compilation units than has use for
them. The principal access to this data is the SVGTests::isValid()
method, so only the actual bindings should need any deeper insight into
these. Shuffle declarations and definitions to make their inclusion more
scarce. (From ~194 -> ~13 total dependencies for the latter, based on
"ninja -t deps".)

Review-Url: https://codereview.chromium.org/2360383003
Cr-Commit-Position: refs/heads/master@{#420614}
7 files changed