test: Use googletest 1.10

This change uses googletest 1.10, which adds `GTEST_SKIP()` to better
signal that a test is being skipped.

Bug: None
Test: make clean && make tests

Change-Id: I63a8eba2a6c0be0ceaab208030f05ba6e8535f4e
diff --git a/Makefile b/Makefile
index c13c099..b7022b5 100644
--- a/Makefile
+++ b/Makefile
@@ -199,7 +199,7 @@
 ifeq ($(USE_SYSTEM_GTEST),no)
 # Points to the root of Google Test, relative to where this file is.
 # Remember to tweak this if you move this file.
-GTEST_DIR = googletest-release-1.8.0/googletest
+GTEST_DIR = googletest-release-1.10.0/googletest
 
 # Flags passed to the preprocessor.
 # Set Google Test's header directory as a system directory, such that