This CL introduces SimpleSplittingSubstitutionMap to allow easier
debugging. This is a simple combination of the SimpleSubstitutionMap
and SplittingSubstitutionMap.

The reason why this is necessary is because
CLOSURE_COMPILED_SPLIT_HYPHENS is really the only
--output_renaming_map_format that *fully* works, based on my
testing. But there doesn't seem to be a way to use the SPLIT_HYPHENS
mode so that the class renames are still human-readable (with the
trailing underscore) for debugging purposes. These classes solve
this problem:

  --output_renaming_map_format=CLOSURE_COMPILED_SPLIT_HYPHENS
  --css_substitution_map_provider=com.google.common.css.SimpleSplittingSubstitutionMapProvider

  goog.setCssNameMapping({
    "kd": "kd_",
    "button": "button_",
  });

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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=78028032
Remove all warnings for vendor-prefixed flex box properties.

These tend to be used for cross-browser backwards compatibility, so
the warnings are causing unwanted noise which obscures genuine
warnings. (Retain the warnings for the unprefixed properties though
since these were never implemented by any browser, at least that was
my understanding and seems to be inline with the note on
https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Flexible_boxes.)
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=78073007