Factor out glyph position computations in SVGTextQuery
Factor out glyph position computations in SVGTextQuery

In preparation for fixing RTL handling, move some common code for
computing the position of a glyph into two helper functions.

No functional changes.

BUG=470326

Review URL: https://codereview.chromium.org/1032603005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@192624 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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