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/decode_test_driver.h b/test/decode_test_driver.h
index b8f8d1a..153ff5d 100644
--- a/test/decode_test_driver.h
+++ b/test/decode_test_driver.h
@@ -12,7 +12,7 @@
 #ifndef TEST_DECODE_TEST_DRIVER_H_
 #define TEST_DECODE_TEST_DRIVER_H_
 #include <cstring>
-#include "third_party/googletest/src/include/gtest/gtest.h"
+#include "third_party/googletest/src/googletest/include/gtest/gtest.h"
 #include "./aom_config.h"
 #include "aom/aom_decoder.h"