liblogcat: measure performance

Existing dummy benchmark converted to a single-pass benchmark.

Add support for ">[filename]" interpretation in liblogcat, helpful to
provide more consistent benchmark results when sending output to
/dev/null.

NB: results are not consistent as there is a roundtrip to logd
    service, but they are indicative of better performance for
    liblogcat.

Benchmark                                Time           CPU Iterations
----------------------------------------------------------------------
BM_logcat_stat_popen_libc         35221677 ns     603314 ns        100
BM_logcat_stat_popen_liblogcat    15871805 ns     579398 ns       1287
BM_logcat_stat_system_libc        39037825 ns     319882 ns        100
BM_logcat_stat_system_liblogcat    9896755 ns     762610 ns       1310
BM_logcat_dump_popen_libc        776206254 ns  131448772 ns          5
BM_logcat_dump_popen_liblogcat   610674905 ns  118709624 ns          6
BM_logcat_dump_system_libc       512191254 ns     388724 ns         10
BM_logcat_dump_system_liblogcat  443897570 ns  377215696 ns          2

Test: logcat-benchmarks --benchmark_filter='BM_logcat_stat*|BM_logcat_dump*'
Bug: 35326290
Change-Id: Ie94900a3070487f45742f6c0789b5b3cf036df34
diff --git a/logcat/tests/Android.mk b/logcat/tests/Android.mk
index 1c3feba..22aca17 100644
--- a/logcat/tests/Android.mk
+++ b/logcat/tests/Android.mk
@@ -27,11 +27,12 @@
     -fno-builtin \
 
 # -----------------------------------------------------------------------------
-# Benchmarks (actually a gTest where the result code does not matter)
+# Benchmarks
 # ----------------------------------------------------------------------------
 
 benchmark_src_files := \
-    logcat_benchmark.cpp
+    logcat_benchmark.cpp \
+    exec_benchmark.cpp \
 
 # Build benchmarks for the device. Run with:
 #   adb shell /data/nativetest/logcat-benchmarks/logcat-benchmarks
@@ -40,7 +41,8 @@
 LOCAL_MODULE_TAGS := $(test_tags)
 LOCAL_CFLAGS += $(test_c_flags)
 LOCAL_SRC_FILES := $(benchmark_src_files)
-include $(BUILD_NATIVE_TEST)
+LOCAL_SHARED_LIBRARIES := libbase liblogcat
+include $(BUILD_NATIVE_BENCHMARK)
 
 # -----------------------------------------------------------------------------
 # Unit tests.