Misc. small cleanups.

* Better param names
* Avoid using negative values for (bogus) placeholder channel counts (mostly in tests).  Since channels will be changing to size_t, negative values will be illegal; it's sufficient to use 0 in these cases.
* Use arraysize()
* Use size_t for counting frames, samples, blocks, buffers, and bytes -- most of these are already size_t in most places, this just fixes some stragglers
* reinterpret_cast<int64_t>(void*) is not necessarily safe; use uintptr_t instead
* Remove unnecessary code, e.g. dead code, needlessly long/repetitive code, or function overrides that exactly match the base definition
* Fix indenting
* Use uint32_t for timestamps (matching how it's already a uint32_t in most places)
* Spelling
* RTC_CHECK_EQ(expected, actual)
* Rewrap
* Use .empty()
* Be more pedantic about matching int/int32_t/
* Remove pointless consts on input parameters to functions
* Add missing sanity checks

All this was found in the course of constructing https://codereview.webrtc.org/1316523002/ , and is being landed separately first.

BUG=none
TEST=none

Review URL: https://codereview.webrtc.org/1534193008

Cr-Commit-Position: refs/heads/master@{#11191}

webrtc/modules/audio_coding/include/audio_coding_module.h

@@ -134,7 +134,7 @@ class AudioCodingModule {
   //    0 if succeeded.
   //
   static int Codec(const char* payload_name, CodecInst* codec,
-                       int sampling_freq_hz, int channels);
+                   int sampling_freq_hz, int channels);
 
   ///////////////////////////////////////////////////////////////////////////
   // int32_t Codec()
@@ -153,7 +153,7 @@ class AudioCodingModule {
   //   -1 if the codec is not found.
   //
   static int Codec(const char* payload_name, int sampling_freq_hz,
-                             int channels);
+                   int channels);
 
   ///////////////////////////////////////////////////////////////////////////
   // bool IsCodecValid()