Support joined -D flags for gn.

BUG=326230
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/145073004

git-svn-id: http://src.chromium.org/svn/trunk/src/build@246558 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

gyp_chromium

@@ -121,8 +121,11 @@ def GetGypVarsForGN(supplemental_files):
   # to ignore all arguments other than "-D".
   cmdline_input_items = []
   for i in range(len(sys.argv))[1:]:
-    if sys.argv[i] == '-D' and i + 1 < len(sys.argv):
-      cmdline_input_items += [sys.argv[i + 1]]
+    if sys.argv[i].startswith('-D'):
+      if sys.argv[i] == '-D' and i + 1 < len(sys.argv):
+        cmdline_input_items += [sys.argv[i + 1]]
+      elif len(sys.argv[i]) > 2:
+        cmdline_input_items += [sys.argv[i][2:]]
   cmdline_items = ProcessGypDefinesItems(cmdline_input_items)
 
   return dict(supp_items + env_items + cmdline_items)