We could try turning off
enable_dice_support which I see is currently
enabled on Fuchsia by default (likely for the deprecated Fuchsia Workstation project). That might reduce our binary size as well.
I gave it a quick try locally, but found that we're pulling in //components/signin and the compiler is unhappy.
gen/third_party/libc++/src/include/__memory/unique_ptr.h:75:19: error: invalid application of 'sizeof' to an incomplete type 'ProfileOAuth2TokenServiceDelegate'
From gn path, looks like signin/identity_manager is pulled in by GCM, which (correct me if I'm wrong Zijie) is needed for your current work?
$ gn path out/arm //fuchsia_web/webengine:web_engine_exe //components/signin/internal/identity_manager
//fuchsia_web/webengine:web_engine_exe --[private]-->
//fuchsia_web/webengine:web_engine_core --[private]-->
//components/gcm_driver:gcm_driver --[private]-->
//components/signin/public/identity_manager:identity_manager --[private]-->
//components/signin/internal/identity_manager:identity_manager
David