Gzip save files for multistage compilation

The save files scale linearly with the size of the application and can thus be quite large. By gzipping we can reduce sizes substantially, which should save disk space.  Gzip is fairly fast and given that we can expect a reduction in file-io as a result this may or may not be a wall time regression.

PiperOrigin-RevId: 511888713

Author: lukesandberg

src/com/google/javascript/jscomp/Compiler.java

@@ -119,6 +119,8 @@
 import java.util.logging.Logger;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
+import java.util.zip.GZIPInputStream;
+import java.util.zip.GZIPOutputStream;
 import org.jspecify.nullness.Nullable;
 
 /**
@@ -4035,12 +4037,16 @@ public void saveState(OutputStream outputStream) throws IOException {
     runInCompilerThread(
         () -> {
           Tracer tracer = newTracer("serializeCompilerState");
-          new ObjectOutputStream(outputStream).writeObject(getCompilerState());
+          GZIPOutputStream gzipStream = new GZIPOutputStream(outputStream);
+          new ObjectOutputStream(gzipStream).writeObject(getCompilerState());
           stopTracer(tracer, "serializeCompilerState");
           tracer = newTracer("serializeTypedAst");
-          SerializeTypedAstPass.createFromOutputStream(this, outputStream)
+          SerializeTypedAstPass.createFromOutputStream(this, gzipStream)
               .process(externsRoot, jsRoot);
           stopTracer(tracer, "serializeTypedAst");
+          // Finish will flush all zip buffers and write out zip trailing bytes but it will not
+          // close the stream since that is our callers responsibility.
+          gzipStream.finish();
           return null;
         });
   }
@@ -4059,7 +4065,7 @@ public void restoreState(InputStream inputStream) throws IOException, ClassNotFo
           Tracer tracer = newTracer(PassNames.DESERIALIZE_COMPILER_STATE);
           logger.fine("Deserializing the CompilerState");
           try {
-            deserializeCompilerState(inputStream);
+            deserializeCompilerState(new GZIPInputStream(inputStream));
             return null;
           } finally {
             logger.fine("Finished deserializing CompilerState");