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If we call GetProperty of kAudioUnitProperty_StreamFormat before setting the format, the device will report kAudioFormatFlagsNativeFloatPacked | kLinearPCMFormatFlagIsNonInterleaved as the native format of the device, which is the same as the output.

This patch changes the format to use kAudioFormatFlagsNativeFloatPacked | kLinearPCMFormatFlagIsNonInterleaved to open the device, so that we will avoid format flipping back and forth. Hope this optimization will help increase the stability of the input audio on Mac.

BUG=404884
TEST=media_unittests && https://webrtc.googlecode.com/svn-history/r5497/trunk/samples/js/demos/html/pc1.html, https://www.google.com/intl/en/chrome/demos/speech.html

Review URL: https://codereview.chromium.org/501823002

Cr-Commit-Position: refs/heads/master@{#292151}