[debug] Ensure there are source positions when debugging

This fixes ~15 debug/inspector tests that were failing when
v8_enable_lazy_source_positions = true.

Bug: v8:8510
Change-Id: Ica02aa2ea84549b5cddd82b5b98835829f7b0f1b
Reviewed-on: https://chromium-review.googlesource.com/c/1477280
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59695}

src/debug/debug.cc

@@ -1503,6 +1503,8 @@ void Debug::CreateBreakInfo(Handle<SharedFunctionInfo> shared) {
   if (CanBreakAtEntry(shared)) flags |= DebugInfo::kCanBreakAtEntry;
   debug_info->set_flags(flags);
   debug_info->set_break_points(*break_points);
+
+  SharedFunctionInfo::EnsureSourcePositionsAvailable(isolate_, shared);
 }
 
 Handle<DebugInfo> Debug::GetOrCreateDebugInfo(