Add validator for chrome binary

[masutaka]

Hi Heroku,

I added validator for chrome binary. We can avoid missing libs error such as #56.

This change gives the following logs.

remote: -----> Validating google-chrome binary
remote:        Google Chrome 74.0.3729.169 unknown

You can try the invalid case with the following patch.

diff --git a/bin/compile b/bin/compile
index 4b69ba2..28671ad 100755
--- a/bin/compile
+++ b/bin/compile
@@ -185,4 +185,5 @@ export GOOGLE_CHROME_SHIM="\$HOME/.apt/usr/bin/$SHIM"
 EOF

 topic "Validating google-chrome binary"
+rm $BUILD_DIR/.apt/usr/lib/x86_64-linux-gnu/libnss3.so
 $BUILD_DIR/.apt/opt/google/$BIN --version | indent

Deployment fails with the following error. Users can avoid releasing invalid Chrome binary.

remote: -----> Validating google-chrome binary
remote: /tmp/build_4ce8259a990331c321050350bde9d177/.apt/opt/google/chrome/chrome: error while loading shared libraries: libnss3.so: cannot open shared object file: No such file or directory
remote:  !     Push rejected, failed to compile Google Chrome app.
remote:
remote:  !     Push failed

[masutaka]

@joshwlewis Could you review it?