[serializer] clear debug info for code cache.

Debug info carries more information than just break points. It also carries
debugging-related flags and data for block coverage and type profiling.

In production we won't run into the situation where debug info is created with
the debugger not enabled. But this way seems a bit more robust.

Bug: v8:7396
Change-Id: I6989bbab82a3c597a43dde382a74114f945adf5f
Reviewed-on: https://chromium-review.googlesource.com/898923Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51057}

src/snapshot/code-serializer.cc

@@ -134,14 +134,16 @@ void CodeSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
     // TODO(7110): Enable serializing of Asm modules once the AsmWasmData
     // is context independent.
     DCHECK(!sfi->IsApiFunction() && !sfi->HasAsmWasmData());
-    // Do not serialize when a debugger is active.
-    DCHECK(sfi->debug_info()->IsSmi());
+    // Clear debug info.
+    Object* debug_info = sfi->debug_info();
+    sfi->set_debug_info(Smi::kZero);
 
     // Mark SFI to indicate whether the code is cached.
     bool was_deserialized = sfi->deserialized();
     sfi->set_deserialized(sfi->is_compiled());
     SerializeGeneric(obj, how_to_code, where_to_point);
     sfi->set_deserialized(was_deserialized);
+    sfi->set_debug_info(debug_info);
     return;
   }