Re-enable doc uploading on Travis (#11118)

https://github.com/flutter/flutter/issues/10940

.travis.yml

 os:
   - linux
 sudo: false
+filter_secrets: false
 addons:
   apt:
     # sky_shell binary depends on /usr/lib/x86_64-linux-gnu/libstdc++.so.6 version GLIBCXX_3.4.18
@@ -22,8 +23,7 @@ env:
 before_script:
   - ./dev/bots/travis_setup.sh
 script:
-  # TODO(tvolkert): Re-enable `&& ./dev/bots/travis_upload.sh`
-  - (./bin/cache/dart-sdk/bin/dart ./dev/bots/test.dart)
+  - (./bin/cache/dart-sdk/bin/dart ./dev/bots/test.dart && ./dev/bots/travis_upload.sh)
 cache:
   directories:
     - $HOME/.pub-cache

dev/bots/travis_setup.sh

@@ -5,11 +5,10 @@ echo $KEY_FILE | base64 --decode > ../gcloud_key_file.json
 
 set -x
 
-# TODO(tvolkert): Re-enable once this is able to successfully run on Travis
-#if [ -n "$TRAVIS" ] && [ "$TRAVIS_PULL_REQUEST" == "false" ]; then
-#  export CLOUDSDK_CORE_DISABLE_PROMPTS=1
-#  curl https://sdk.cloud.google.com | bash
-#fi
+if [ -n "$TRAVIS" ]; then
+  export CLOUDSDK_CORE_DISABLE_PROMPTS=1
+  curl https://sdk.cloud.google.com | bash
+fi
 
 # disable analytics on the bots and download Flutter dependencies
 ./bin/flutter config --no-analytics