Fix limit on size of glyph paths.

Fix limit on size of glyph paths.

Some web fonts have been observed to contain glyphs which require a buffer
greater than 20KB. In these rare cases we should allocate space on the heap.
Most glyphs require less than 8KB, and Windows has a 1MB stack, so in the
common case just use the stack.

This change also removes the gFTMutex which was both poorly named and used.
The constructor does not appear to have any need for it, and with this change
the path generation code does not need it. The mask generating code does need
memory barriers for correctness, but these bariers are no-ops on x86. We will
need another change to clean up this sort of static initialization code.

R=caryclark@google.com

Review URL: https://codereview.chromium.org/17435003

git-svn-id: http://skia.googlecode.com/svn/trunk@9700 2bbb7eff-a529-9590-31e7-b0007b416f81