Improve unit tests for trace writers

* New unit test suite for interceptor_trace_writer.
* Changes to trace_writer_impl_unittest:
  * Couple of new tests.
  * Minor cleanups:
    * Remove redundant SharedMemoryArbiterImpl construction.
    * Avoid stringstream to build large strings.
    * Avoid yoda comparisons in EXPECT and ASSERT.
    * Use EXPECT instead of ASSERT where possible.
    * Use SizeIs() matcher. This makes it clear that we're asserting the
      size of an array before accessing its elements.

Change-Id: I9e347fde690c2e7c54eea2a5d3cc12233dae0bd4
diff --git a/Android.bp b/Android.bp
index 381211a..a7c4677 100644
--- a/Android.bp
+++ b/Android.bp
@@ -9398,6 +9398,7 @@
 filegroup {
     name: "perfetto_src_tracing_unittests",
     srcs: [
+        "src/tracing/internal/interceptor_trace_writer_unittest.cc",
         "src/tracing/traced_proto_unittest.cc",
         "src/tracing/traced_value_unittest.cc",
     ],