Move SVGTextMetricsCalculator to LayoutSVGInlineText.cpp

Mostly plain code move, with some fixups in the (now folded)
updateMetricsList method. Also removes the non-const getter for the
metrics list.

BUG=594058

Review URL: https://codereview.chromium.org/1879453003

Cr-Commit-Position: refs/heads/master@{#386630}
5 files changed