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}

webrtc/modules/audio_coding/neteq/background_noise.cc

@@ -239,7 +239,7 @@ void BackgroundNoise::SaveParameters(size_t channel,
   parameters.low_energy_update_threshold = 0;
 
   // Normalize residual_energy to 29 or 30 bits before sqrt.
-  int norm_shift = WebRtcSpl_NormW32(residual_energy) - 1;
+  int16_t norm_shift = WebRtcSpl_NormW32(residual_energy) - 1;
   if (norm_shift & 0x1) {
     norm_shift -= 1;  // Even number of shifts required.
   }
@@ -251,7 +251,8 @@ void BackgroundNoise::SaveParameters(size_t channel,
   // Add 13 to the |scale_shift_|, since the random numbers table is in
   // Q13.
   // TODO(hlundin): Move the "13" to where the |scale_shift_| is used?
-  parameters.scale_shift = 13 + ((kLogResidualLength + norm_shift) / 2);
+  parameters.scale_shift =
+      static_cast<int16_t>(13 + ((kLogResidualLength + norm_shift) / 2));
 
   initialized_ = true;
 }