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Re-land: http://review.webrtc.org/2151007/ TBR=bjornv@webrtc.org Original change description: This mode extends the filter length from the current 48 ms to 128 ms. It is runtime selectable which allows it to be enabled through experiment. We reuse the DelayCorrection infrastructure to avoid having to replumb everything up to libjingle. Increases AEC complexity by ~50% on modern x86 CPUs. Measurements (in percent of usage on one core): Machine/CPU Normal Extended MacBook Retina (Early 2013), Core i7 Ivy Bridge (2.7 GHz, hyperthreaded) 0.6% 0.9% MacBook Air (Late 2010), Core 2 Duo (2.13 GHz) 1.4% 2.7% Chromebook Pixel, Core i5 Ivy Bridge (1.8 GHz) 0.6% 1.0% Samsung ARM Chromebook, Samsung Exynos 5 Dual (1.7 GHz) 3.2% 5.6% The relative value is large of course but the absolute should be acceptable in order to have a working AEC on some platforms. Detailed changes to the algorithm: - The filter length is changed from 48 to 128 ms. This comes with tuning of several parameters: i) filter adaptation stepsize and error threshold; ii) non-linear processing smoothing and overdrive. - Option to ignore the reported delays on platforms which we deem sufficiently unreliable. Currently this will be enabled in Chromium for Mac. - Faster startup times by removing the excessive "startup phase" processing of reported delays. - Much more conservative adjustments to the far-end read pointer. We smooth the delay difference more heavily, and back off from the difference more. Adjustments force a readaptation of the filter, so they should be avoided except when really necessary. Corresponds to these changes: https://chromereviews.googleplex.com/9412014 https://chromereviews.googleplex.com/9514013 https://chromereviews.googleplex.com/9960013 BUG=454,827,1261 Review URL: https://webrtc-codereview.appspot.com/2295006 git-svn-id: http://webrtc.googlecode.com/svn/trunk@4848 4adac7df-926f-26a2-2b94-8c16560cd09d