Add google benchmark submodule to third_party.

Let's do some benchmarking!

Bug: b/148660286
Change-Id: I1e0e9b0ec7cf1cba689d195a176eebaf418c8b56
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40808
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
diff --git a/.gitmodules b/.gitmodules
index 6f9424d..d010d48 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,19 +1,18 @@
 [submodule "third_party/cppdap"]
 	path = third_party/cppdap
 	url = https://github.com/google/cppdap
-
 [submodule "third_party/googletest"]
 	path = third_party/googletest
 	url = https://github.com/google/googletest.git
-
 [submodule "third_party/json"]
 	path = third_party/json
 	url = https://github.com/nlohmann/json.git
-
 [submodule "third_party/libbacktrace/src"]
 	path = third_party/libbacktrace/src
 	url = https://github.com/ianlancetaylor/libbacktrace.git
-
 [submodule "third_party/PowerVR_Examples"]
 	path = third_party/PowerVR_Examples
 	url = https://github.com/powervr-graphics/Native_SDK.git
+[submodule "third_party/benchmark"]
+	path = third_party/benchmark
+	url = https://github.com/google/benchmark.git
diff --git a/third_party/benchmark b/third_party/benchmark
new file mode 160000
index 0000000..e5ea03c
--- /dev/null
+++ b/third_party/benchmark
@@ -0,0 +1 @@
+Subproject commit e5ea03ce07997620980636b3ee7e6117d68bc6ad