Add support for constrained windows on os x, based on Avi's GTMWindowSheetController.

DEPS

 vars = {
   "webkit_trunk":
     "http://svn.webkit.org/repository/webkit/trunk",
   "webkit_revision": "47034",
 }
 
 
 deps = {
   "src/breakpad/src":
     "http://google-breakpad.googlecode.com/svn/trunk/src@346",
@@ skipping 76 matching lines @@
       "/trunk/deps/third_party/cygwin@11984",
 
     "src/third_party/python_24":
       "/trunk/deps/third_party/python_24@22967",
 
     "src/third_party/ffmpeg/binaries/chromium":
       "/trunk/deps/third_party/ffmpeg/binaries/win@22838",
   },
   "mac": {
     "src/third_party/GTM":
-      "http://google-toolbox-for-mac.googlecode.com/svn/trunk@170",
+      "http://google-toolbox-for-mac.googlecode.com/svn/trunk@171",
     "src/third_party/pdfsqueeze":
       "http://pdfsqueeze.googlecode.com/svn/trunk@2",
     "src/third_party/WebKit/WebKit/mac":
       Var("webkit_trunk") + "/WebKit/mac@" + Var("webkit_revision"),
     "src/third_party/WebKit/WebKitLibraries":
       Var("webkit_trunk") + "/WebKitLibraries@" + Var("webkit_revision"),
     "src/third_party/ffmpeg/binaries/chromium":
       "/trunk/deps/third_party/ffmpeg/binaries/mac@22838",
   },
   "unix": {
@@ skipping 42 matching lines @@
     # A change to a .gyp, .gypi, or to GYP itself shound run the generator.
     "pattern": "\\.gypi?$|[/\\\\]src[/\\\\]tools[/\\\\]gyp[/\\\\]",
     "action": ["python", "src/tools/gyp/gyp_chromium"],
   },
   {
     # Workaround IncrediBuild problem. http://crbug.com/17706.
     "pattern": "\\.grd$",
     "action": ["python", "src/build/win/clobber_generated_headers.py", "$matching_files"],
   },
 ]