Add benchmark library

Add https://github.com/google/benchmark to buildtools with matching
BUILD rules and an example under libtracing/hello_world_benchmark.cc.

Change-Id: Iba39983a6e2b69f0706d0996202802a9cfce3f10
diff --git a/build/install-build-deps b/build/install-build-deps
index be1e33b..0769e07 100755
--- a/build/install-build-deps
+++ b/build/install-build-deps
@@ -95,6 +95,13 @@
    '4072e8fd76febee37f60aeda76d6d9f5e3791daa',
    'all'
   ),
+
+  # Benchmarking tool.
+  ('buildtools/benchmark.zip',
+   'https://github.com/google/benchmark/archive/v1.2.0.zip',
+   '553b6bfa59c63f15c54cfd8c5122b0f7f84469af',
+   'all'
+  ),
 ]
 
 # Dependencies required to build Android code.