Merge 661693003 to M39: Avoid reporting 0 as input level when AudioProcessing zero out the audio da…

Merge 661693003 to M39: Avoid reporting 0 as input level when AudioProcessing zero out the audio data
Avoid reporting 0 as input level when AudioProcessing zero out the audio data.

When the microphone volume is low, the pre-processed audio data contains energy, while the post-processed audio data has only 0, we report 0 as energy before this patch, which is wrong since the audio flow contains energy.

This patch fix the problem by checking the energy of pre-processed data before reporting 0 as energy.

TBR=tommi@chromium.org

BUG=424149
TEST=1, use a USB headset.
2, set the microphone volume low, like below 50%.
3, join a hangout call.
4, open chrome://webrtc-internals, and look at the energy of input stream, constantly it is 0 there.

Committed: https://chromium.googlesource.com/chromium/src/+/da6c91364a2c062353432e8138f6b472b24b558a

[no longer working on chromium, 2014-10-23 10:08:39]

Committed patchset #1 (id:1) manually as
da6c91364a2c062353432e8138f6b472b24b558a (presubmit successful).