Include googletest cmake support.

- Same googletest release (v1.8.0), new root in third_party.
- Update Android.mk and make build (include and file locations).
- Update cmake build (use googletest's cmake support).
- Update gtest include in all tests.

BUG=https://bugs.chromium.org/p/aomedia/issues/detail?id=76

Change-Id: I5491a2ff3c8869263cd885872c815402236c20b1
diff --git a/test/av1_dct_test.cc b/test/av1_dct_test.cc
index defecb2..691cc8b 100644
--- a/test/av1_dct_test.cc
+++ b/test/av1_dct_test.cc
@@ -13,7 +13,7 @@
 #include <stdlib.h>
 #include <new>
 
-#include "third_party/googletest/src/include/gtest/gtest.h"
+#include "third_party/googletest/src/googletest/include/gtest/gtest.h"
 #include "test/acm_random.h"
 #include "test/util.h"
 #include "./aom_config.h"