Added first version of the EchoControl interface, used for AEC abstraction.

Bug: webrtc:8346
Change-Id: I792a5f8eefb98388de199fea12c017759fdc6c1e
Reviewed-on: https://webrtc-review.googlesource.com/6780
Reviewed-by: Per Åhgren <peah@webrtc.org>
Commit-Queue: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20174}

modules/audio_processing/include/audio_processing.h

@@ -939,6 +939,21 @@ class EchoControlMobile {
   virtual ~EchoControlMobile() {}
 };
 
+// Interface for an acoustic echo cancellation (AEC) submodule.
+class EchoControl {
+ public:
+  // Analysis (not changing) of the render signal.
+  virtual void AnalyzeRender(AudioBuffer* render) = 0;
+
+  // Analysis (not changing) of the capture signal.
+  virtual void AnalyzeCapture(AudioBuffer* capture) = 0;
+
+  // Processes the capture signal in order to remove the echo.
+  virtual void ProcessCapture(AudioBuffer* capture, bool echo_path_change) = 0;
+
+  virtual ~EchoControl() {}
+};
+
 // The automatic gain control (AGC) component brings the signal to an
 // appropriate range. This is done by applying a digital gain directly and, in
 // the analog mode, prescribing an analog gain to be applied at the audio HAL.