[d8] Fix file name resolution for dynamic imports.

When executing a script that does import("foo"), "foo" should be
relative to the script's directory, not relative to the current working
directory of the d8 process.

R=gsathya@chromium.org

Bug: v8:5785
Change-Id: Id6ceccb242905bd6b54b07038ece60b93d92e4a0
Reviewed-on: https://chromium-review.googlesource.com/546375
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46185}

src/d8.cc

@@ -812,9 +812,11 @@ void Shell::DoHostImportModuleDynamically(void* import_data) {
 
   std::string source_url = ToSTLString(referrer);
   std::string dir_name =
-      IsAbsolutePath(source_url) ? DirName(source_url) : GetWorkingDirectory();
+      DirName(IsAbsolutePath(source_url)
+                  ? source_url
+                  : NormalizePath(source_url, GetWorkingDirectory()));
   std::string file_name = ToSTLString(specifier);
-  std::string absolute_path = NormalizePath(file_name.c_str(), dir_name);
+  std::string absolute_path = NormalizePath(file_name, dir_name);
 
   TryCatch try_catch(isolate);
   try_catch.SetVerbose(true);