If I run
ninja -C out/Debug system_webview_shell_apk -j 1000


then I change content/browser/frame_host/navigator_impl.cc, I get
jam@jabdelmalek:/ssd/android/src$ ninja -C out/Debug system_webview_shell_apk -j 1000
ninja: Entering directory `out/Debug'
ninja: no work to do.


If I do build "content", then it notices it has to be rebuilt.