[DO NOT MERGE ANYWHERE] Add swipes left method in Background.java

Bug: 153276032
Test: TF_GLOBAL_CONFIG=/google/src/cloud/<ldap>/<workspace>/google3/wireless/android/test_tools/forrest/configs/local-host-config.xml \
pts-tradefed run commandAndExit cuj/<testname> \
--primary-abi-only \
--log-level verbose --log-level-display verbose \
--wifi-network GoogleGuest

Change-Id: Ib1cbc609f47a547f173e8170f00af9e8bdfa77bb