Use glyph-ids for lookups of SVG font kerning-pairs

This CL eliminates the SVGTextMetrics::Glyph class in favor
of a simple Glyph (glyph-id). This shrinks SVGTextMetrics
objects by two pointers, and avoids the allocation of tiny
(often single-character/code-unit) strings.

It achieves this by replacing the linear kerning-pair lookup
with a table (HashMap) indexed by a key made up of the glyph id's of the two glyphs.

Review URL: https://codereview.chromium.org/181443002

git-svn-id: svn://svn.chromium.org/blink/trunk@168007 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Replace Apple styled spinner icon with Chromium one.

Drive-by: replace animated PNG files with a CSS animation.

R=yurys@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=167914

Review URL: https://codereview.chromium.org/181433002

git-svn-id: svn://svn.chromium.org/blink/trunk@168008 bbb929c8-8fbe-4397-9dbb-9b2b20218538