gn: gyp_flag_compare.py de-escape command line properly

gn: gyp_flag_compare.py de-escape command line properly

Makes some Skia flags be matched properly.

e.g.

  '-DGR_GL_CUSTOM_SETUP_HEADER="GrGLConfig_chrome.h"'
vs
  -DGR_GL_CUSTOM_SETUP_HEADER=\"GrGLConfig_chrome.h\"

Diffs 393202 -> 374424.

It does make the script quite a bit slower unfortunately, I guess the
regular split is native C.

BUG=335824
Committed: https://crrev.com/8034e1d4dc0524ef8477e475b771c4b080e6dce2
Cr-Commit-Position: refs/heads/master@{#295562}

[scottmg, 2014-09-18 19:57:08]

scottmg@chromium.org changed reviewers:
+ brettw@chromium.org

[brettw, 2014-09-18 20:14:46]

lgtm

[scottmg, 2014-09-18 20:16:27]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2014-09-18 20:18:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/580213003/1

[commit-bot: I haz the power, 2014-09-18 21:45:44]

Committed patchset #1 (id:1) as ba24037b1b8782d4838e97431e33191db710c03c

[commit-bot: I haz the power, 2014-09-18 21:46:50]

Patchset 1 (id:??) landed as
https://crrev.com/8034e1d4dc0524ef8477e475b771c4b080e6dce2
Cr-Commit-Position: refs/heads/master@{#295562}