[Chromecast] Audio output buffer size can be configurable using gn args.

Bug: b:126783022
Test: CQ Presubmit and verified header files are correct.
Change-Id: I0b7c6f97b6191a7c28fa20e470d3718e079925fb
Reviewed-on: https://chromium-review.googlesource.com/c/1496437
Commit-Queue: Alex Leung <alexleung@google.com>
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636872}

chromecast/media/audio/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
-
+import("//build/buildflag_header.gni")
 import("//chromecast/chromecast.gni")
 import("//media/media_options.gni")
 
+declare_args() {
+  # Defines bounds for the output buffer size (in frames)
+  minimum_output_buffer_size_in_frames = 512
+  maximum_output_buffer_size_in_frames = 8192
+  default_output_buffer_size_in_frames = 2048
+}
+
 cast_source_set("audio") {
   sources = [
     "cast_audio_manager.cc",
@@ -16,6 +23,7 @@ cast_source_set("audio") {
   ]
 
   deps = [
+    ":audio_buildflags",
     "//base",
     "//chromecast/base",
     "//chromecast/common/mojom",
@@ -63,3 +71,13 @@ source_set("fake_external_audio_pipeline") {
     "//chromecast/public/media",
   ]
 }
+
+buildflag_header("audio_buildflags") {
+  header = "audio_buildflags.h"
+
+  flags = [
+    "MINIMUM_OUTPUT_BUFFER_SIZE_IN_FRAMES=$minimum_output_buffer_size_in_frames",
+    "MAXIMUM_OUTPUT_BUFFER_SIZE_IN_FRAMES=$maximum_output_buffer_size_in_frames",
+    "DEFAULT_OUTPUT_BUFFER_SIZE_IN_FRAMES=$default_output_buffer_size_in_frames",
+  ]
+}

chromecast/media/audio/cast_audio_manager.cc

@@ -12,6 +12,7 @@
 #include "base/location.h"
 #include "base/logging.h"
 #include "build/build_config.h"
+#include "chromecast/media/audio/audio_buildflags.h"
 #include "chromecast/media/audio/cast_audio_mixer.h"
 #include "chromecast/media/audio/cast_audio_output_stream.h"
 #include "chromecast/media/cma/backend/cma_backend_factory.h"
@@ -28,11 +29,13 @@ namespace {
 const int kDefaultSampleRate = 48000;
 
 // Define bounds for the output buffer size (in frames).
-// Note: These values are copied from AudioManagerPulse implementation.
 // TODO(alokp): Query the preferred value from media backend.
-static const int kMinimumOutputBufferSize = 512;
-static const int kMaximumOutputBufferSize = 8192;
-static const int kDefaultOutputBufferSize = 2048;
+static const int kMinimumOutputBufferSize =
+    BUILDFLAG(MINIMUM_OUTPUT_BUFFER_SIZE_IN_FRAMES);
+static const int kMaximumOutputBufferSize =
+    BUILDFLAG(MAXIMUM_OUTPUT_BUFFER_SIZE_IN_FRAMES);
+static const int kDefaultOutputBufferSize =
+    BUILDFLAG(DEFAULT_OUTPUT_BUFFER_SIZE_IN_FRAMES);
 
 // TODO(jyw): Query the preferred value from media backend.
 static const int kDefaultInputBufferSize = 1024;