Add missing closing namespace comments to wtf.

clang-format strips the newline before the closing '}' of a namespace if
there is no namespace comment.  Since we want these comments anyhow, just
add them.

Patch created by running:
# create compile_commands.json for clang-tidy:
cd src
ninja -C out/Release/ -t compdb objcxx cxx > compile_commands.json
# run clang-tidy check for adding namespace comments:
cd out/Release
~/src/llvm-rw/tools/clang/tools/extra/clang-tidy/tool/run-clang-tidy.py \
    -checks=-*,google-readability-namespace-comments -p ../.. \
    -clang-tidy-binary ~/src/llvm-build/bin/clang-tidy -fix \
    third_party/WebKit/Source/wtf

I then manually reverted changes to two base headers due to
http://llvm.org/PR26274

No behavior change.
BUG=580787,403854

Review URL: https://codereview.chromium.org/1629693002

Cr-Commit-Position: refs/heads/master@{#371143}
27 files changed