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 90e8f52e482e1bd31ccdfc7a1cced2f341271d6f..8e206fba67108cc80e5ffac2ada7003dd10b5cc0 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.
@@ -21,7 +23,8 @@ declare_args() {
   # Higher numbers than 100 does not reduce wall clock compile times
   # even for 4 cores or less so no reason to go (much) higher than 100.
   # 100 uses 8% less total CPU than 50 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 50 is smaller.
   jumbo_file_merge_limit = 100
 }
 
@@ -47,6 +50,14 @@ 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) {
@@ -65,8 +76,11 @@ 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
@@ -255,3 +269,21 @@ set_defaults("jumbo_component") {
     configs = default_compiler_configs
   }
 }
+
+# See documentation above by "internal_jumbo_target".
+template("jumbo_test") {
+  internal_jumbo_target(target_name) {
+    target_type = "test"
+    forward_variables_from(invoker, "*")
+  }
+}
+
+set_defaults("jumbo_test") {
+  if (is_android) {
+    configs = default_shared_library_configs
+    configs -= [ "//build/config/android:hide_all_but_jni_onload" ]
+    configs += [ "//build/config/android:hide_all_but_jni" ]
+  } else {
+    configs = default_executable_configs
+  }
+}