Run the ClangTidy analyser on the AudioProcessing submodule of WebRTC.

This CL contains automatically applied fixes suggested by the
ClangTidy analyzer (http://clang.llvm.org/extra/clang-tidy/). The
following kinds of fixes is present:

* renaming variables when the names in the method signature don't
  match the names in the method definition
  (ClangTidy:readability-inconsistent-declaration-parameter-name)

* ClangTidy:readability-container-size-empty,
  ClangTidy:misc-unused-using-decls,
  ClangTidy:performance-unnecessary-value-param,
  ClangTidy:readability-redundant-control-flow

This is a 'pilot' CL to check if automatic code analyzers can
feasibly be integrated into the WebRTC infrastructuve.

The renamings have been manually expected for consistency with 
surrounding code. In echo_cancellation.cc, I changed several names in
the function implementation to match the function declaration. The
tool suggested changing everything to match the function definitions
instead.

Bug: None
Change-Id: Id3b7ba18c51f15b025f26090c7bdcc642e48d8fd
Reviewed-on: https://chromium-review.googlesource.com/635766
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Alex Loiko <aleloi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19630}

webrtc/modules/audio_processing/audio_processing_impl_unittest.cc

@@ -17,7 +17,6 @@
 #include "webrtc/test/gtest.h"
 
 using ::testing::Invoke;
-using ::testing::Return;
 
 namespace webrtc {
 namespace {