Add google-benchmark to the manifest

It is used by bionic/benchmarks

Change-Id: I3ee14229cd28c6e6d7aba960d52ca33a8aad65f2
diff --git a/default.xml b/default.xml
index e21861a..9abd321 100644
--- a/default.xml
+++ b/default.xml
@@ -68,6 +68,7 @@
   <project path="external/fec" name="platform/external/fec" groups="bdk" />
   <project path="external/flac" name="platform/external/flac" groups="bdk" />
   <project path="external/gmock" name="platform/external/gmock" groups="bdk" />
+  <project path="external/google-benchmark" name="platform/external/google-benchmark" groups="bdk" />
   <project path="external/google-breakpad" name="platform/external/google-breakpad" groups="dragon,bdk" />
   <project path="external/gtest" name="platform/external/gtest" groups="bdk" />
   <project path="external/icu" name="platform/external/icu" groups="bdk" />