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

build/config/jumbo.gni

Index: build/config/jumbo.gni
diff --git a/build/config/jumbo.gni b/build/config/jumbo.gni
index a16795aee1ee2fe0da9aa6c070c6987c3dbcc706..7203bff690f5e4971b27f08c0df4b9b8216220d9 100644
--- a/build/config/jumbo.gni
+++ b/build/config/jumbo.gni
@@ -3,11 +3,13 @@
 # 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.
@@ -19,9 +21,10 @@ declare_args() {
   #
   # 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
 }
 
@@ -46,6 +49,14 @@ declare_args() {
 #      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) {
@@ -64,8 +75,11 @@ template("internal_jumbo_target") {
   }
 
   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
@@ -194,6 +208,7 @@ set_defaults("jumbo_target") {
 # See documentation above by "internal_jumbo_target".
 template("jumbo_component") {
   internal_jumbo_target(target_name) {
+    target_type = "component"
     forward_variables_from(invoker, "*")
   }
 }