[HostStubGen] Use buffered output

Just realized FileOutputStream wasn't buffered. Doh.

This change makes the non-sharded version reasonably faster, but
12x sharding still seems to give a better result, so we'll keep it.

Flag: EXEMPT host side test change only
Bug: 292141694
Test: atest RavenwoodBivalentTest

Change-Id: Ief4f97b1c6f40fb901308aab0a812d731324b002
diff --git a/tools/hoststubgen/hoststubgen/src/com/android/hoststubgen/HostStubGen.kt b/tools/hoststubgen/hoststubgen/src/com/android/hoststubgen/HostStubGen.kt
index c510eee..cb4db57 100644
--- a/tools/hoststubgen/hoststubgen/src/com/android/hoststubgen/HostStubGen.kt
+++ b/tools/hoststubgen/hoststubgen/src/com/android/hoststubgen/HostStubGen.kt
@@ -37,6 +37,7 @@
 import org.objectweb.asm.commons.Remapper
 import org.objectweb.asm.util.CheckClassAdapter
 import java.io.BufferedInputStream
+import java.io.BufferedOutputStream
 import java.io.FileOutputStream
 import java.io.InputStream
 import java.io.OutputStream
@@ -273,7 +274,7 @@
         if (filename == null) {
             return block(null)
         }
-        return ZipOutputStream(FileOutputStream(filename)).use(block)
+        return ZipOutputStream(BufferedOutputStream(FileOutputStream(filename))).use(block)
     }
 
     /**