Move Skia's variables and defines to skia_common.

Move Skia's variables and defines to skia_common.

skia_library_opts was not being compiled with any of these defines.  Now it is.

Testing:
  1) build/gyp_chromium && ninja -C out/Debug
  2) Looked for Skia defines in .ninja files

master:
$ grep -l DSK *.ninja
filter_fuzz_stub.ninja
image_operations_bench.ninja
skia_chrome.ninja
skia_library.ninja

this CL:
$ grep -l DSK *.ninja
filter_fuzz_stub.ninja
image_operations_bench.ninja
skia_chrome.ninja
skia_library.ninja
skia_opts.ninja
skia_opts_none.ninja
skia_opts_ssse3.ninja

BUG=
R=bungeman@google.com

Review URL: https://codereview.chromium.org/98503006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241394 0039d316-1c4b-4281-b951-d872f2087c98