Update sdk/platform-tools to version 26.0.0.

Command used to update:
rm -rf sdk/platform-tools &&
  wget https://dl.google.com/android/repository/platform-tools-latest-linux.zip &&
  unzip platform-tools-latest-linux.zip -d sdk &&
  rm platform-tools-latest-linux.zip && git add .

Bug: 735481
Change-Id: I7e14e2ca832d73a0613fb5d51d1442247618f584
Reviewed-on: https://chromium-review.googlesource.com/615163
Reviewed-by: John Budorick <jbudorick@chromium.org>