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/obmc_sad_test.cc b/test/obmc_sad_test.cc
index 1814cdd..811c35b 100644
--- a/test/obmc_sad_test.cc
+++ b/test/obmc_sad_test.cc
@@ -9,7 +9,7 @@
  * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
  */
 
-#include "third_party/googletest/src/include/gtest/gtest.h"
+#include "third_party/googletest/src/googletest/include/gtest/gtest.h"
 
 #include "test/function_equivalence_test.h"
 #include "test/register_state_check.h"