Allow Script::FindSharedFunctionInfo to return toplevel functions

We will use this function to find toplevel function infos in an upcoming
commit.

R=yangguo@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/1970153002
Cr-Commit-Position: refs/heads/master@{#36204}

src/compiler.cc

@@ -1546,6 +1546,7 @@ Handle<SharedFunctionInfo> Compiler::GetSharedFunctionInfo(
   // unless we already have code with debut break slots.
   Handle<SharedFunctionInfo> existing;
   if (maybe_existing.ToHandle(&existing) && existing->is_compiled()) {
+    DCHECK(!existing->is_toplevel());
     if (!outer_info->is_debug() || existing->HasDebugCode()) {
       return existing;
     }

src/objects.cc

@@ -12408,9 +12408,6 @@ MaybeHandle<SharedFunctionInfo> Script::FindSharedFunctionInfo(
     if (fun->function_token_position() == shared->function_token_position() &&
         fun->start_position() == shared->start_position() &&
         fun->end_position() == shared->end_position()) {
-      // This method is not used to find top-level SharedFunctionInfo objects,
-      // verify that above checks are sufficient to distinguish top-level code.
-      DCHECK(!shared->is_toplevel());
       return Handle<SharedFunctionInfo>(shared);
     }
   }