Add third_party/google_benchmark to cronet's copybara

Test: None
Change-Id: Id390c6c53f619b7bc87c80ae08acca9ee3a65c2e
diff --git a/Cronet/tools/import/copy.bara.sky b/Cronet/tools/import/copy.bara.sky
index a73779a..5ae4a6b 100644
--- a/Cronet/tools/import/copy.bara.sky
+++ b/Cronet/tools/import/copy.bara.sky
@@ -87,6 +87,8 @@
         # Note: Only used for tests.
         "third_party/ced/**",
         # Note: Only used for tests.
+        "third_party/google_benchmark/**",
+        # Note: Only used for tests.
         "third_party/googletest/**",
         "third_party/icu/**",
         "third_party/libc++/**",