Snapshot of all changes to get jumbo in blink and content.

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
+import("//testing/test.gni")  # When someone uses the test target_type
 
 declare_args() {
   # If true, use a jumbo build (files compiled together) to speed up
-  # compilation.
-  use_jumbo_build = false
+  # compilation. Enabled by default for everything official builds and
+  # Android+gcc builds because of a warning that prevents builds.
+  use_jumbo_build = !is_official_build && !(is_android && !is_clang)
 
   # A target to exclude from jumbo builds, for optimal round trip time
   # when frequently changing a single cpp file.
   jumbo_build_excluded = ""
 
   # How many files to group at most. Smaller numbers give more
   # parallellism, higher numbers give less total CPU usage. Higher
   # numbers also give longer single-file recompilation times.
   #
   # Recommendations:
   # Higher numbers than 200 does not reduce wall clock compile times
-  # for 4 cores or less.
+  # even for 4 cores or less so no reason to go (much) higher than 200.
   # 200 uses 8% less total CPU than 100 when compiling content and 10%
-  # less wall clock when compiling with 4 cores.
+  # less wall clock when compiling with 4 cores but content is extreme so
+  # the total negative effect of 100 is smaller.
   jumbo_file_merge_limit = 200
 }
 
 # Use one of the targets jumbo_target or jumbo_component to generate a
 # target which merges sources if possible to compile much faster.
 #
 # Special values.
 #
 #   target_type
 #      The kind of target to build. For example the string
 #      "static_library".
 #
 #   always_build_jumbo
 #      If set and set to true, then use jumbo compile even when it is
 #      globally disabled. Otherwise it has no effect.
 #
 #   never_build_jumbo
 #      If set and set to true, then do not jumbo compile even if it is
 #      globally enabled. Otherwise it has no effect.
 #
 #   jumbo_excluded_sources
 #      If set to a list of files, those files will not be merged with
 #      the rest. This can be necessary if merging the files causes
 #      compilation issues and fixing the issues is impractical.
+#
+#   jumbo_gen_dir
+#      If set, this overrides the default location for the generated
+#      jumbo files. This can be needed if the default location is too
+#      deep for the build tools. By default the location is based on
+#      the first file in sources. (Might not be neeeded one Chromium
+#      has the fix for
+#      https://github.com/ninja-build/ninja/issues/1161.
 template("internal_jumbo_target") {
   use_jumbo_build_for_target = use_jumbo_build
   if (defined(invoker.always_build_jumbo) && invoker.always_build_jumbo) {
     use_jumbo_build_for_target = true
   }
   if (defined(invoker.never_build_jumbo) && invoker.never_build_jumbo) {
     use_jumbo_build_for_target = false
   }
   if (target_name == jumbo_build_excluded) {
     use_jumbo_build_for_target = false
   }
 
   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".
+  if (defined(invoker.jumbo_gen_dir)) {
+    gen_target_dir = invoker.jumbo_gen_dir
+  } else {
+    gen_target_dir = get_path_info(invoker_sources[0], "gen_dir")
+  }
 
   # 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")
@@ skipping 108 matching lines @@
 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
 }
 
 # See documentation above by "internal_jumbo_target".
 template("jumbo_component") {
   internal_jumbo_target(target_name) {
+    target_type = "component"
     forward_variables_from(invoker, "*")
   }
 }
 
 set_defaults("jumbo_component") {
   # This sets the default list of configs when the content_source_set
   # target is defined. This code is a clone of set_defaults for the
   # ordinary "component" template.
   if (is_component_build) {
     configs = default_shared_library_configs
     if (is_android) {
       configs -= [ "//build/config/android:hide_all_but_jni_onload" ]
     }
   } else {
     configs = default_compiler_configs
   }
 }