[Chromecast] Make sure to process audio frames in multiples of 8 in tests

The mixer ensures this in actual operation, and some postprocessors
assume that the frame count is divisible by 8.

Change-Id: I8fb5cd808c0e481f9a19e77c96595023e1320112
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2616867Reviewed-by: Yuchen Liu <yucliu@chromium.org>
Commit-Queue: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841306}

chromecast/media/cma/backend/mixer/post_processors/post_processor_unittest.cc

@@ -166,7 +166,10 @@ void TestRingingTime(AudioPostProcessor2* pp,
   int frames_remaining = status.ringing_time_frames;
   int frames_to_process = std::min(frames_remaining, kNumFrames);
   while (frames_remaining > 0) {
+    // Make sure |frames_to_process| is an even multiple of 8.
     frames_to_process = std::min(frames_to_process, frames_remaining);
+    frames_to_process = (frames_to_process + 7);
+    frames_to_process -= frames_to_process % 8;
     data.assign(frames_to_process * num_input_channels, 0);
     pp->ProcessFrames(data.data(), frames_to_process, &metadata);
     frames_remaining -= frames_to_process;