Add curly braces to control statements in modules/webaudio.

Not all of these are to fix coding style guide violations, but some are.  Regardless of the style guide, including the braces in all control statements will make it easier to identify branches and also easier to modify the code more safely in the future.

This change was performed automatically using clang-tidy with the following steps:

1) Add the following to custom_vars in .gclient:  'checkout_clang_tidy': True,

2) Run: gclient runhooks

3) Build chromium and change to the build output directory (path_to_chromium/src/out/Default for me)

4) Run the following: gn gen . --export-compile-commands

5) Run the following command from the modules/webaudio directory: path_to_chromium/src/third_party/llvm-build/Release+Asserts/bin/clang-tidy -p path_to_chromium/src/out/Default -checks="-*,readability-braces-around-statements" -fix *.cc *.h

6) Run: git cl format

Reference: https://chromium.googlesource.com/chromium/src/+/HEAD/docs/clang_tidy.md

This change should NOT cause any performance or behavior changes.

Change-Id: I9fd70a545704f883cfb0e204fe45e39bd1da17ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3369279
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Michael Wilson <mjwilson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#957815}