Create a standalone ebuild for system_api

system_api is required by a lot of platform2 packages. We need it to be in a
standalone ebuild in order for other packages to depend on it.

This package installs the common headers and compiles the protobufs into static
libraries.

BUG=chromium:386223
TEST=FEATURES=test emerge-amd64-generic platform2.
TEST=trybot run on daisy, link, duck, x86-mario.
TEST=trybot run on lumpy-incremental-release.

CQ-DEPEND=CL:204594

Change-Id: I96a0745cbb96a7ea8bf1fa14c92a408175254e98
Reviewed-on: https://chromium-review.googlesource.com/204604
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>
diff --git a/system_api/system_api.pc b/system_api/system_api.pc
new file mode 100644
index 0000000..c6925ac
--- /dev/null
+++ b/system_api/system_api.pc
@@ -0,0 +1,4 @@
+Name: system_api
+Description: Protobuffers and headers shared by Chromium OS and Chromium.
+Version: 0.1
+Libs: -lsystem_api-power_manager-protos -lsystem_api-cryptohome-protos -lsystem_api-protos