Preserve explicit dimensions on <use>'d <symbol>

Per [1], 'width' and/or 'height' on a <use> override the corresponding
values on a referenced <svg> or <symbol>. If no 'width' or 'height' is
specified on the <use>, the values set on the referenced elements are
retained.
Previously we would always set 'width' / 'height' on a referenced
<symbol> to '100%' if the <use> did not have any overriding values.
Change this to follow the specification and copy the values from the
original element as needed - much like what was previously done for
referenced <svg> elements.

[1] https://svgwg.org/svg2-draft/struct.html#UseLayout

Bug: 806289
Change-Id: Iaf595ff88af2865a080f95ccc414e283828c195e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1530883
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#642150}
9 files changed