base: extract Event class for eventfd/pipe

Extracts a common class to wrap eventfd and its pipe-based
fallback for Mac. This is going to be used for the iorap work
and hence hit the "three strikes and you refactor" rule.

Bug: 116547201
Change-Id: I1d6f2bb5aaab32f2dd4e3d888b3409e8f8df276c
diff --git a/Android.bp b/Android.bp
index 541e66f..480e618 100644
--- a/Android.bp
+++ b/Android.bp
@@ -32,6 +32,7 @@
     ":perfetto_protos_perfetto_trace_trusted_lite_gen",
     ":perfetto_protos_perfetto_trace_zero_gen",
     ":perfetto_src_ipc_wire_protocol_gen",
+    "src/base/event.cc",
     "src/base/file_utils.cc",
     "src/base/metatrace.cc",
     "src/base/page_allocator.cc",
@@ -157,6 +158,7 @@
     ":perfetto_src_ipc_wire_protocol_gen",
     ":perfetto_src_perfetto_cmd_protos_gen",
     "src/base/android_task_runner.cc",
+    "src/base/event.cc",
     "src/base/file_utils.cc",
     "src/base/metatrace.cc",
     "src/base/page_allocator.cc",
@@ -297,6 +299,7 @@
     ":perfetto_protos_perfetto_trace_zero_gen",
     ":perfetto_src_ipc_wire_protocol_gen",
     "src/base/android_task_runner.cc",
+    "src/base/event.cc",
     "src/base/file_utils.cc",
     "src/base/metatrace.cc",
     "src/base/page_allocator.cc",
@@ -3612,6 +3615,7 @@
     ":perfetto_protos_perfetto_trace_trusted_lite_gen",
     ":perfetto_protos_perfetto_trace_zero_gen",
     ":perfetto_src_ipc_wire_protocol_gen",
+    "src/base/event.cc",
     "src/base/file_utils.cc",
     "src/base/metatrace.cc",
     "src/base/page_allocator.cc",
@@ -3800,6 +3804,7 @@
     ":perfetto_src_traced_probes_ftrace_test_messages_lite_gen",
     ":perfetto_src_traced_probes_ftrace_test_messages_zero_gen",
     "src/base/android_task_runner.cc",
+    "src/base/event.cc",
     "src/base/file_utils.cc",
     "src/base/metatrace.cc",
     "src/base/page_allocator.cc",
@@ -4033,6 +4038,7 @@
     ":perfetto_protos_perfetto_trace_minimal_lite_gen",
     ":perfetto_protos_perfetto_trace_ps_lite_gen",
     ":perfetto_protos_perfetto_trace_sys_stats_lite_gen",
+    "src/base/event.cc",
     "src/base/file_utils.cc",
     "src/base/metatrace.cc",
     "src/base/page_allocator.cc",