Build issue seems to be introduced by this change: 
https://chromium-review.googlesource.com/c/chromium/src/+/983972


In this builder: 
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Android%20FYI%2064%20Vk%20Release%20(Nexus%205X)

Example of the logs: 

/b/swarming/w/ir/cache/builder/src/buildtools/linux64/gn gen //out/Release --check --runtime-deps-list-file=/b/swarming/w/ir/cache/builder/src/out/Release/runtime_deps
  -> returned 1
ERROR at //base/BUILD.gn:1802:33: Undefined identifier in string expansion.
    "CAN_UNWIND_WITH_CFI_TABLE=$can_unwind_with_cfi_table",