Use jinja2 templating engine for Python code generators

Source/core/core.gypi

 {
     'variables': {
         'core_idl_files': [
             'css/CSSCharsetRule.idl',
             'css/CSSFontFaceLoadEvent.idl',
             'css/CSSFontFaceRule.idl',
             'css/CSSHostRule.idl',
             'css/CSSImportRule.idl',
             'css/CSSMediaRule.idl',
             'css/CSSPageRule.idl',
@@ skipping 3649 matching lines @@
         'core_unittest_files': [
             'tests/HeapGraphSerializerTest.cpp',
             'tests/LayoutUnit.cpp',
             'tests/LinkRelAttribute.cpp',
             'tests/WebSocketPerMessageDeflateTest.cpp'
         ],
         'scripts_for_in_files': [
             'scripts/in_file.py',
             'scripts/in_generator.py',
             'scripts/license.py',
+            'scripts/template_expander.py',
         ],
         'conditions': [
             ['OS=="win"', {
                 # Using native perl rather than cygwin perl cuts execution time
                 # of idl preprocessing rules by a bit more than 50%.
                 'perl_exe': '<(DEPTH)/third_party/perl/perl/bin/perl.exe',
                 'gperf_exe': '<(DEPTH)/third_party/gperf/bin/gperf.exe',
                 'bison_exe': '<(DEPTH)/third_party/bison/bin/bison.exe',
                 # Using cl instead of cygwin gcc cuts the processing time from
                 # 1m58s to 0m52s.
                 'preprocessor': '--preprocessor "cl.exe -nologo -EP -TP"',
               },{
                 'perl_exe': 'perl',
                 'gperf_exe': 'gperf',
                 'bison_exe': 'bison',
                 # We specify a preprocess so it happens locally and won't get
                 # distributed to goma.
                 # FIXME: /usr/bin/gcc won't exist on OSX forever. We want to
                 # use /usr/bin/clang once we require Xcode 4.x.
                 'preprocessor': '--preprocessor "/usr/bin/gcc -E -P -x c++"'
               }],
          ],
     }
 }