[Fuchsia] Fix SysmemBufferWriter to use recommended buffer size

Previously SysmemBufferWriter::GetRecommendedConstraints() was using
has_per_packet_buffer_bytes_recommended() result as min_size_bytes, i.e.
min_size_bytes was set to 1, which is obviously incorrect.

Bug: 1003651
Change-Id: I64cc94b3dcc46d226d7fd6432aa91dcb49b76902
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1808092
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Yuchen Liu <yucliu@chromium.org>
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Yuchen Liu <yucliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696997}

media/fuchsia/common/sysmem_buffer_writer.cc

@@ -174,8 +174,13 @@ SysmemBufferWriter::GetRecommendedConstraints(
   buffer_constraints.min_buffer_count_for_camping =
       stream_constraints.default_settings().packet_count_for_client();
   buffer_constraints.has_buffer_memory_constraints = true;
+
+  const int kDefaultPacketSize = 512 * 1024;
   buffer_constraints.buffer_memory_constraints.min_size_bytes =
-      stream_constraints.has_per_packet_buffer_bytes_recommended();
+      stream_constraints.has_per_packet_buffer_bytes_recommended()
+          ? stream_constraints.per_packet_buffer_bytes_recommended()
+          : kDefaultPacketSize;
+
   buffer_constraints.buffer_memory_constraints.ram_domain_supported = true;
   buffer_constraints.buffer_memory_constraints.cpu_domain_supported = true;