Determine used fonts based on the correct font code path

InspectorCSSAgent previously always instantiated a SimpleShaper,
leading to incorrect results when the run was shaped using complex
path.

BUG=538180
R=eae,lushnikov

Review URL: https://codereview.chromium.org/1379473005

Cr-Commit-Position: refs/heads/master@{#352311}
3 files changed