Match existing type usage better.

This makes a variety of small changes to synchronize bits of code using different types, remove useless code or casts, and add explicit casts in some places previously doing implicit ones.  For example:

* Change a few type declarations to better match how the majority of code uses those objects.
* Eliminate "< 0" check for unsigned values.
* Replace "(float)sin(x)", where |x| is also a float, with "sinf(x)", and similar.
* Add casts to uint32_t in many places timestamps were used and the existing code stored signed values into the unsigned objects.
* Remove downcasts when the results would be passed to a larger type, e.g. calling "foo((int16_t)x)" with an int |x| when foo() takes an int instead of an int16_t.
* Similarly, add casts when passing a larger type to a function taking a smaller one.
* Add casts to int16_t when doing something like "int16_t = int16_t + int16_t" as the "+" operation would implicitly upconvert to int, and similar.
* Use "false" instead of "0" for setting a bool.
* Shift a few temp types when doing a multi-stage calculation involving typecasts, so as to put the most logical/semantically correct type possible into the temps.  For example, when doing "int foo = int + int; size_t bar = (size_t)foo + size_t;", we might change |foo| to a size_t and move the cast if it makes more sense for |foo| to be represented as a size_t.

BUG=none
R=andrew@webrtc.org, asapersson@webrtc.org, henrika@webrtc.org, juberti@webrtc.org, kwiberg@webrtc.org
TBR=andrew, asapersson, henrika

Review URL: https://codereview.webrtc.org/1168753002

Cr-Commit-Position: refs/heads/master@{#9419}
diff --git a/webrtc/modules/audio_coding/neteq/test/RTPencode.cc b/webrtc/modules/audio_coding/neteq/test/RTPencode.cc
index c097f5f..192d374 100644
--- a/webrtc/modules/audio_coding/neteq/test/RTPencode.cc
+++ b/webrtc/modules/audio_coding/neteq/test/RTPencode.cc
@@ -621,8 +621,8 @@
       }
 
       /* write RTP packet to file */
-      length = htons(12 + enc_len + 8);
-      plen = htons(12 + enc_len);
+      length = htons(static_cast<unsigned short>(12 + enc_len + 8));
+      plen = htons(static_cast<unsigned short>(12 + enc_len));
       offset = (uint32_t)sendtime;  //(timestamp/(fs/1000));
       offset = htonl(offset);
       if (fwrite(&length, 2, 1, out_file) != 1) {
@@ -673,7 +673,7 @@
           memmove(&rtp_data[RTPheaderLen + red_len[0]], &rtp_data[12], enc_len);
           memcpy(&rtp_data[RTPheaderLen], red_data, red_len[0]);
 
-          red_len[1] = enc_len;
+          red_len[1] = static_cast<uint16_t>(enc_len);
           red_TS[1] = timestamp;
           if (vad)
             red_PT[1] = payloadType;
@@ -689,7 +689,7 @@
           memmove(&rtp_data[RTPheaderLen - 4], &rtp_data[12], enc_len);
           // memcpy(&rtp_data[RTPheaderLen], red_data, red_len[0]);
 
-          red_len[1] = enc_len;
+          red_len[1] = static_cast<uint16_t>(enc_len);
           red_TS[1] = timestamp;
           if (vad)
             red_PT[1] = payloadType;
@@ -714,8 +714,8 @@
       do {
 #endif  // MULTIPLE_SAME_TIMESTAMP
         /* write RTP packet to file */
-        length = htons(12 + enc_len + 8);
-        plen = htons(12 + enc_len);
+        length = htons(static_cast<unsigned short>(12 + enc_len + 8));
+        plen = htons(static_cast<unsigned short>(12 + enc_len));
         offset = (uint32_t)sendtime;
         //(timestamp/(fs/1000));
         offset = htonl(offset);