perfetto: add minimal implementation of Streams

This CL adds a minimal implementation of streams in the Perfetto
codebase. This is mainly intended to be used by cloud trace processor.

This is largely analogous to aosp/2381492 which introduced futures.

Change-Id: I9809dbf67320ae7103373470206e2829023ab159
diff --git a/Android.bp b/Android.bp
index 7392a26..ce5b623 100644
--- a/Android.bp
+++ b/Android.bp
@@ -8182,6 +8182,7 @@
 filegroup {
     name: "perfetto_src_base_threading_threading",
     srcs: [
+        "src/base/threading/stream_combinators.cc",
         "src/base/threading/thread_pool.cc",
     ],
 }
@@ -8192,6 +8193,7 @@
     srcs: [
         "src/base/threading/channel_unittest.cc",
         "src/base/threading/future_unittest.cc",
+        "src/base/threading/stream_unittest.cc",
         "src/base/threading/thread_pool_unittest.cc",
     ],
 }