Invalidate DDC library cache on trackLibraries

Since we cache everything on the first call to
`_computeLibraryMetadata`, if we haven't called `trackLibraries` for
some module before the first time we fetch libraries then it will never
be available.

Change-Id: If0c8d5835fb95e244797631d6452bd154eec30e5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/120936
Reviewed-by: Vijay Menon <vsm@google.com>
Commit-Queue: Nate Bosch <nbosch@google.com>

Author: natebosch

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/rtti.dart

@@ -152,6 +152,9 @@ void trackLibraries(
   JS('', '#.set(#, #)', _loadedSourceMaps, moduleName, sourceMap);
   JS('', '#.set(#, #)', _loadedModules, moduleName, libraries);
   JS('', '#.set(#, #)', _loadedPartMaps, moduleName, parts);
+  _libraries = null;
+  _libraryObjects = null;
+  _parts = null;
 }
 
 List<String> _libraries;

sdk_nnbd/lib/_internal/js_dev_runtime/private/ddc_runtime/rtti.dart

@@ -154,6 +154,9 @@ void trackLibraries(
   JS('', '#.set(#, #)', _loadedSourceMaps, moduleName, sourceMap);
   JS('', '#.set(#, #)', _loadedModules, moduleName, libraries);
   JS('', '#.set(#, #)', _loadedPartMaps, moduleName, parts);
+  _libraries = null;
+  _libraryObjects = null;
+  _parts = null;
 }
 
 List<String> _libraries;