Move most of FontRenderStyle manipulation code into its own file
This CL isolates FontPlatformData::m_style handling into its
method, so that m_style is easy to move from FontPlatformData
to SimpleFontData.
BUG=
608650
Committed:
https://crrev.com/fe669432f4eca6a0948012858b459fd2631a72da
Cr-Commit-Position: refs/heads/master@{#392494}