Cleanup: Forward declare AudioFrame type in voiceprocess.h

No need to include this header since the API is just taking a pointer to
it.

BUG=1092
TEST=./webrtc/build/gyp_webrtc && ninja -C out/Debug
R=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/44059004

Patch from Thiago Farina <tfarina@chromium.org>.

Cr-Commit-Position: refs/heads/master@{#8928}

talk/media/base/voiceprocessor.h

@@ -28,12 +28,13 @@
 #ifndef TALK_MEDIA_BASE_VOICEPROCESSOR_H_
 #define TALK_MEDIA_BASE_VOICEPROCESSOR_H_
 
-#include "talk/media/base/audioframe.h"
 #include "webrtc/base/basictypes.h"
 #include "webrtc/base/sigslot.h"
 
 namespace cricket {
 
+class AudioFrame;
+
 enum MediaProcessorDirection {
     MPD_INVALID = 0,
     MPD_RX = 1 << 0,

talk/media/webrtc/webrtcvoiceengine.cc

@@ -38,6 +38,7 @@
 #include <string>
 #include <vector>
 
+#include "talk/media/base/audioframe.h"
 #include "talk/media/base/audiorenderer.h"
 #include "talk/media/base/constants.h"
 #include "talk/media/base/streamparams.h"