Add a simple, safe gain PostProcessor.

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 b87f10a5b548c8b489f55016d0ed8336f8992f57..ea6399b19fe37f5c77286b625f705bb7bdecdd33 100644
--- a/chromecast/media/cma/backend/alsa/BUILD.gn
+++ b/chromecast/media/cma/backend/alsa/BUILD.gn
@@ -27,6 +27,7 @@ shared_library("libcast_media_1.0_audio") {
 
   deps = [
     ":alsa_cma_backend",
+    ":post_processor_factory",
     "//base",
     "//chromecast/base",
     "//chromecast/public",
@@ -64,6 +65,7 @@ source_set("alsa_cma_backend") {
   deps = [
     ":alsa_features",
     ":slew_volume",
+    ":volume_map",
     "//base",
     "//chromecast/base",
     "//chromecast/media/base",
@@ -76,6 +78,19 @@ source_set("alsa_cma_backend") {
   ]
 }
 
+source_set("volume_map") {
+  sources = [
+    "cast_audio_json.cc",
+    "cast_audio_json.h",
+    "volume_map.cc",
+    "volume_map.h",
+  ]
+  deps = [
+    "//base",
+    "//chromecast/base",
+  ]
+}
+
 source_set("slew_volume") {
   sources = [
     "slew_volume.cc",
@@ -101,14 +116,24 @@ buildflag_header("alsa_features") {
 test("cast_alsa_cma_backend_unittests") {
   sources = [
     "filter_group_unittest.cc",
+    "post_processors/governor_unittest.cc",
+    "post_processors/saturated_gain_unittest.cc",
+    "slew_volume_unittests.cc",
     "stream_mixer_alsa_unittest.cc",
   ]
 
   deps = [
+    ":governor",
+    ":libcast_governor_1.0",
+    ":libcast_saturated_gain_1.0",
+    ":post_processor_factory",
+    ":post_processor_test_support",
+    ":slew_volume",
     ":test_support",
     "//base",
     "//base/test:run_all_unittests",
     "//chromecast/media",
+    "//chromecast/public",
     "//media",
     "//media:shared_memory_support",
     "//testing/gmock",
@@ -135,51 +160,44 @@ source_set("test_support") {
   ]
 }
 
-test("slew_volume_unittests") {
+# This is separate from ":governor" because the associated unittest needs
+# to create a Governor directly (to use test functions).
+shared_library("libcast_governor_1.0") {
   sources = [
-    "slew_volume_unittests.cc",
+    "post_processors/governor_create.cc",
   ]
-  deps = [
-    ":slew_volume",
-    "//base",
-    "//base/test:run_all_unittests",
-    "//media",
-    "//testing/gtest",
-  ]
-}
-
-shared_library("libcast_governor_1.0") {
   deps = [
     ":governor",
+    "//chromecast/public/media",
   ]
 }
 
-test("libcast_governor_unittests") {
+source_set("governor") {
   sources = [
-    "post_processors/governor_unittest.cc",
+    "post_processors/governor.cc",
+    "post_processors/governor.h",
   ]
   deps = [
-    ":governor",
-    ":post_processor_test_support",
+    ":slew_volume",
     "//base",
-    "//base/test:run_all_unittests",
-    "//media",
-    "//testing/gtest",
+    "//chromecast/base",
+    "//chromecast/public/media",
   ]
+  public_configs = [ "//chromecast/public:public_config" ]
 }
 
-source_set("governor") {
+shared_library("libcast_saturated_gain_1.0") {
   sources = [
-    "post_processors/governor.cc",
-    "post_processors/governor.h",
+    "post_processors/saturated_gain.cc",
+    "post_processors/saturated_gain.h",
   ]
   deps = [
     ":slew_volume",
+    ":volume_map",
     "//base",
     "//chromecast/base",
     "//chromecast/public/media",
   ]
-  public_configs = [ "//chromecast/public:public_config" ]
 }
 
 source_set("post_processor_test_support") {
@@ -194,3 +212,14 @@ source_set("post_processor_test_support") {
     "//testing/gtest",
   ]
 }
+
+source_set("post_processor_factory") {
+  sources = [
+    "post_processor_factory.cc",
+    "post_processor_factory.h",
+  ]
+  deps = [
+    "//base",
+    "//chromecast/public/media",
+  ]
+}