protobuf: Allow disabling public_config propagation in gn targets

When depending on multiple similar proto_library targets, each target
can create its own public_config. In the case of perfetto, this adds up
to about a dozen configs, each adding the exact same include path.

Because gn doesn't eliminate duplicate include paths (crbug.com/gn/142),
these configs end up adding duplicate -I command line flags to build
commands. On some bots, this recently caused us to exceed command line
length limits (see crbug.com/1043279).

This patch adds an invoker argument to the proto_library gn template,
which disables the public_config propgation of the proto_library target
and will allow perfetto to define and propagate a separate
public_config instead to avoid this duplication.

Bug: 1043279, gn:142
Change-Id: Ifa68c164b2b4c631bdaf98f63ba5bf7537e8e166
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2010860
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734043}

third_party/protobuf/proto_library.gni

@@ -99,6 +99,15 @@
 #       A list of config labels that will be removed from the configs apllying
 #       to the source set.
 #
+#   propagate_imports_configs (optional)
+#       A boolean value (defaults to true) that specifies whether the config
+#       generated for the library's import directories will be propagated to
+#       dependents as one of the library target's public_configs. See
+#       crbug.com/1043279#c11 and crbug.com/gn/142 for why this option exists.
+#       WARNING: If set to false, the embedder target is responsible for
+#       propagating a suitable config, so that any dependent headers can resolve
+#       includes generated by proto imports.
+#
 # Example:
 #  proto_library("mylib") {
 #    sources = [
@@ -391,9 +400,19 @@ template("proto_library") {
     if (generate_cc || generate_with_plugin) {
       # Not necessary if all protos are located in the same directory.
       if (has_nested_dirs || defined(invoker.import_dirs)) {
-        # It's not enough to set |include_dirs| for target since public imports
-        # expose corresponding includes to header files as well.
-        public_configs += [ ":$config_name" ]
+        # By default, propagate the config for |include_dirs| to dependent
+        # targets, so that public imports can be resolved to corresponding
+        # header files. In some cases, the embedder target handles include
+        # directory propagation itself, e.g. via a common config.
+        propagate_imports_configs =
+            !defined(invoker.propagate_imports_configs) ||
+            invoker.propagate_imports_configs
+        if (propagate_imports_configs) {
+          public_configs += [ ":$config_name" ]
+        } else {
+          # Embedder handles include directory propagation to dependents.
+          configs += [ ":$config_name" ]
+        }
       }
 
       # If using built-in cc generator, the resulting headers reference headers