Add toSVGRootInlineBox(), and use it as much as we can

It has type checking assertions, and helps to detect wrong type casting.
This cl removes unnecessary local variable as well.

BUG=N/A

Review URL: https://chromiumcodereview.appspot.com/23447021

git-svn-id: svn://svn.chromium.org/blink/trunk@157733 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Special-case only android and windows platforms and for the default case use sysconf() call to get the number of cores.

Review URL: https://chromiumcodereview.appspot.com/23609031

git-svn-id: svn://svn.chromium.org/blink/trunk@157734 bbb929c8-8fbe-4397-9dbb-9b2b20218538