Here is the current code for getting imported libraries which match a prefix:

331 void getImportedLibrariesMatchingPrefix(int32_t libraryId, Dart_Handle prefix, V
      ector<std::pair<Dart_Handle, intptr_t> >* libraries)
  332 {
  333 Dart_Handle imports = Dart_GetLibraryImports(libraryId);
  334 ASSERT(!Dart_IsError(imports));
  335 // Unfortunately dart_debugger_api.h adds a trailing dot to import prefixes.
  336 if (!Dart_IsNull(prefix))
  337 prefix = addTrailingDot(prefix);
  338 intptr_t length = 0;
  339 Dart_ListLength(imports, &length);
  340 for (intptr_t i = 0; i < length; i += 2) {
  341 Dart_Handle importPrefix = Dart_ListGetAt(imports, i);
  342 ASSERT(Dart_IsNull(importPrefix) || Dart_IsString(importPrefix));
  343 bool equals = false;
  344 Dart_Handle result = Dart_ObjectEquals(prefix, importPrefix, &equals);
  345 ASSERT(!Dart_IsError(result));
  346 if (equals) {
  347 Dart_Handle importedLibraryIdHandle = Dart_ListGetAt(imports, i + 1)
      ;
  348 ASSERT(Dart_IsInteger(importedLibraryIdHandle));
  349 int64_t importedLibraryId;
  350 Dart_IntegerToInt64(importedLibraryIdHandle, &importedLibraryId);
  351 Dart_Handle libraryURL = Dart_GetLibraryURL(importedLibraryId);
  352 ASSERT(!Dart_IsError(libraryURL));
  353 Dart_Handle library = Dart_LookupLibrary(libraryURL);
  354 ASSERT(Dart_IsLibrary(library));
  355 libraries->append(std::pair<Dart_Handle, intptr_t>(library, imported
      LibraryId));
  356 }
  357 }
  358 }