Switch gyp_chromium from third_party/python_26, which is gone, to

build/gyp_chromium

Index: build/gyp_chromium
===================================================================
--- build/gyp_chromium	(revision 245662)
+++ build/gyp_chromium	(working copy)
@@ -304,7 +304,8 @@
   # TODO(bradnelson): take this out once this issue is fixed:
   #    http://code.google.com/p/gyp/issues/detail?id=177
   if sys.platform == 'cygwin':
-    python_dir = os.path.join(chrome_src, 'third_party', 'python_26')
+    depot_tools_path = find_depot_tools.add_depot_tools_to_path()
+    python_dir = os.path.join(depot_tools_path, 'python276_bin')

[M-A Ruel, 2014/01/18 00:10:58]

The main issue is that it is not forward compatible. I'd prefer it to search
imediate subdirectories for a python.exe.

[Peter Kasting, 2014/01/18 00:13:23]

The problem here is that there's also a "python_bin" dir which contains a
python.exe that is python 2.6.

I would love to see that directory die, so that "python_bin" was the one and
only python, but I don't know the history of this directory or why that hasn't
been done already.  Until then, I don't know how one would write the
aforementioned search.

[M-A Ruel, 2014/01/18 00:16:40]

python_exe = sorted(glob.glob(os.path.join(depot_tools_path,
'python2*_bin/python.exe')))[-1]

[Peter Kasting, 2014/01/18 00:20:27]

That's certainly a little better, but it still assumes python is in a "python2*"
directory.  Why can't we just kill python_bin and move python276_bin to that?

     env = os.environ.copy()
     env['PATH'] = python_dir + os.pathsep + env.get('PATH', '')
     p = subprocess.Popen(