evdev: Move EventConverterOzone ownership from EventFactoryOzone to subclass

That way, event converters can be organized in whichever way is most useful
for the platform. For evdev, organize by device path. This will let us find
out which which devices have already been opened and is needed for hotplug.

Review URL: https://codereview.chromium.org/133233008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247764 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247764
JSONWriter cleanups falling out from optimization attempts.

As part of issue 330908, I've scrutinized JSONWriter on all angles. Despite failing to optimize it much; here are some micro optimizations and style cleanups I came up with, might as well put them in (although their impact appears to be minimal from local profiling).

BUG=330908

Review URL: https://codereview.chromium.org/139903013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247765 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247765