Add incomplete ResourceAdaptationModuleInterface.

This interface will be improved upon iteratively to aid reviewability.
The initial version only handles starting and stopping the module; input
and output of the module is still implementation-specific.

TBR=sprang@webrtc.org

Bug: webrtc:11222
Change-Id: Ie307cfe3d3211c84346c035f2c0e9a632f58221b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/162580
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@google.com>
Cr-Commit-Position: refs/heads/master@{#30167}
diff --git a/call/adaptation/BUILD.gn b/call/adaptation/BUILD.gn
index 12d04a1..a51f930 100644
--- a/call/adaptation/BUILD.gn
+++ b/call/adaptation/BUILD.gn
@@ -12,6 +12,8 @@
   sources = [
     "resource.cc",
     "resource.h",
+    "resource_adaptation_module_interface.cc",
+    "resource_adaptation_module_interface.h",
     "resource_adaptation_processor.cc",
     "resource_adaptation_processor.h",
     "resource_consumer.cc",