Enable UBSan float-cast-overflow warnings and fix existing ones

webrtc/modules/audio_processing/level_controller/level_controller.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 31 matching lines @@
   for (float& v : x) {
     v -= *dc_level;
   }
 }
 
 float FrameEnergy(const AudioBuffer& audio) {
   float energy = 0.f;
   for (size_t k = 0; k < audio.num_channels(); ++k) {
     float channel_energy =
         std::accumulate(audio.channels_const_f()[k],
-                        audio.channels_const_f()[k] + audio.num_frames(), 0,
+                        audio.channels_const_f()[k] + audio.num_frames(), 0.f,

[saza WebRTC, 2017/09/05 09:35:20]

Good find. Fyi, aleloi@ or hlundin@ are the least busy OWNERs of
audio_processing/ who can lgtm this.

                         [](float a, float b) -> float { return a + b * b; });
     energy = std::max(channel_energy, energy);
   }
   return energy;
 }
 
 float PeakLevel(const AudioBuffer& audio) {
   float peak_level = 0.f;
   for (size_t k = 0; k < audio.num_channels(); ++k) {
     auto* channel_peak_level = std::max_element(
@@ skipping 221 matching lines @@
 
 bool LevelController::Validate(
     const AudioProcessing::Config::LevelController& config) {
   return (config.initial_peak_level_dbfs <
               std::numeric_limits<float>::epsilon() &&
           config.initial_peak_level_dbfs >
               -(100.f + std::numeric_limits<float>::epsilon()));
 }
 
 }  // namespace webrtc