Jumbo for blink/core generated files as well (saving 8 CPU minutes)

build/config/jumbo.gni

 # Copyright 2017 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/split_static_library.gni")  # When someone uses that target_type
 
 declare_args() {
   # If true, use a jumbo build (files compiled together) to speed up
   # compilation.
   use_jumbo_build = false
@@ skipping 48 matching lines @@
   }
 
   excluded_sources = []
   if (defined(invoker.jumbo_excluded_sources)) {
     excluded_sources += invoker.jumbo_excluded_sources
   }
 
   invoker_sources = invoker.sources
   gen_target_dir = get_path_info(invoker_sources[0], "gen_dir")
   assert(excluded_sources != [] || true)  # Prevent "unused variable".
+
+  # Find the gen_target_dir directory with shortest path. Short paths
+  # are nice in themselves since they mean shorter error messages and
+  # fewer bytes to parse, but the currently deployed version of ninja
+  # also has a limitation where it only allows 32 path components in
+  # Windows.
+  # See https://crbug.com/738186 and
+  # https://github.com/ninja-build/ninja/issues/1161
+  foreach(source_file, invoker.sources) {
+    possibly_better_gen_target_dir = get_path_info(gen_target_dir, "dir")
+    possibly_better_gen_target_dir_2 =
+        get_path_info(possibly_better_gen_target_dir, "dir")
+    alt_gen_target_dir = get_path_info(source_file, "gen_dir")
+    if (alt_gen_target_dir == possibly_better_gen_target_dir ||
+        alt_gen_target_dir == possibly_better_gen_target_dir_2) {
+      gen_target_dir = alt_gen_target_dir
+    }
+  }
+
   assert(gen_target_dir != "")  # Prevent "unused variable".
 
   if (use_jumbo_build_for_target) {
     jumbo_files = []
 
     # Split the sources list into chunks that are not excessively large
     files_per_chunk = jumbo_file_merge_limit
     current_file_index = 0
     next_chunk_start = 0
     next_chunk_number = 1
@@ skipping 73 matching lines @@
     forward_variables_from(invoker, "*", variables_to_not_forward)
   }
 }
 
 set_defaults("jumbo_target") {
   # This sets the default list of configs when the content_source_set target
   # is defined. The default_compiler_configs comes from BUILDCONFIG.gn and
   # is the list normally applied to static libraries and source sets.
   configs = default_compiler_configs
 }