* build: define compile time features with buildflag header
* refactor: switch to BUILDFLAG(ENABLE_DESKTOP_CAPTURER)
* refactor: switch to BUILDFLAG(ENABLE_RUN_AS_NODE)
* refactor: switch to BUILDFLAG(ENABLE_OSR)
* refactor: switch to BUILDFLAG(ENABLE_VIEW_API)
* refactor: switch to BUILDFLAG(ENABLE_PEPPER_FLASH)
* refactor: switch to BUILDFLAG(OVERRIDE_LOCATION_PROVIDER)
* refactor: switch to BUILDFLAG(ENABLE_PDF_VIEWER)
* remove unused variable
* limit scope of variable 'ret'
* pass shared_ptr<SkBitmap> by reference
* silence warning: value reassign before read
* fix oops
* don't refer to 'response' after std::move()ing it
* make the linter happy