Add optimized vpx_blend_mask6

This is to replace vp10/common/reconinter.c:build_masked_compound.
Functionality is equivalent, but the interface is slightly more
generic.

Total encoder speedup with ext-inter: ~7.5%

Change-Id: Iee18b83ae324ffc9c7f7dc16d4b2b06adb4d4305

test/function_equivalence_test.h

@@ -0,0 +1,40 @@
+/*
+ *  Copyright (c) 2016 The WebM project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef TEST_FUNCTION_EQUIVALENCE_TEST_H_
+#define TEST_FUNCTION_EQUIVALENCE_TEST_H_
+
+#include "third_party/googletest/src/include/gtest/gtest.h"
+#include "test/clear_system_state.h"
+#include "test/util.h"
+
+namespace libvpx_test {
+template <typename T>
+class FunctionEquivalenceTest :
+  public ::testing::TestWithParam< std::tr1::tuple< T, T > > {
+ public:
+  virtual ~FunctionEquivalenceTest() {}
+
+  virtual void SetUp() {
+    ref_func_ = std::tr1::get<0>(this->GetParam());
+    tst_func_ = std::tr1::get<1>(this->GetParam());
+  }
+
+  virtual void TearDown() {
+    libvpx_test::ClearSystemState();
+  }
+
+ protected:
+  T ref_func_;
+  T tst_func_;
+};
+
+}   // namespace libvpx_test
+#endif  // TEST_FUNCTION_EQUIVALENCE_TEST_H_