Add a general PostProcessorUnittest.

chromecast/media/cma/backend/alsa/BUILD.gn

Index: chromecast/media/cma/backend/alsa/BUILD.gn
diff --git a/chromecast/media/cma/backend/alsa/BUILD.gn b/chromecast/media/cma/backend/alsa/BUILD.gn
index 4de9c9aeeffbfd30df4bcfefd4c175b78fb34391..b38afec23d6552c393d58ef4e60cf2bc79048104 100644
--- a/chromecast/media/cma/backend/alsa/BUILD.gn
+++ b/chromecast/media/cma/backend/alsa/BUILD.gn
@@ -160,8 +160,8 @@ test("libcast_governor_unittests") {
   ]
   deps = [
     ":governor",
+    ":post_processor_test",
     "//base",
-    "//base/test:run_all_unittests",
     "//media",
     "//testing/gtest",
   ]
@@ -180,3 +180,17 @@ source_set("governor") {
   ]
   public_configs = [ "//chromecast/public:public_config" ]
 }
+
+source_set("post_processor_test") {
+  testonly = true
+  sources = [
+    "post_processors/post_processor_unittest.cc",
+    "post_processors/post_processor_unittest.h",
+  ]
+  deps = [
+    "//base",
+    "//base/test:run_all_unittests",

[slan, 2017/06/19 20:50:36]

Why link this in at this level? This means that this can't be linked as even an
indirect dependency of any other target. 

For that matter, why not just add these files to the test target directly?

[bshaya, 2017/06/19 21:22:48]

Removed run_all_unittests as a dependency here.

These files will be included in various parts of the chromecast  where
post-processors are defined, so it is useful to have a source_set for them
(libcast_governor_unittests will not be their only use).

+    "//chromecast/public/media",
+    "//testing/gtest",
+  ]
+}