move_blink_source.py: Rename CSSOMFoo to cssom_foo

instead of css_om_foo.
This CL has no behavior changes.

Bug: 578345
Change-Id: I54e26c53291c7d95611ad6afdff59d49be57d66e
Reviewed-on: https://chromium-review.googlesource.com/963866Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543309}

third_party/blink/tools/blinkpy/common/name_style_converter.py

@@ -20,6 +20,7 @@ SPECIAL_TOKENS = [
     'Uint32',
     'WebGL2',
     'ASCII',
+    'CSSOM',
     'CType',
     'DList',
     'Int16',