cc: Fix error in smoothness_priority_expiration_notifier for ProxyImpl

The error was introduced by https://codereview.chromium.org/1417053005/
where using TimeDelta::FromSeconds for a double value caused the
DelayedUniqueNotifier to be initialized with zero delay.

This also fixes the flakiness for BenchmarkSmokeTest.thread_times on
Win7 bots, caused by an increase in the number of trace events from the
DelayedUniqueNotifier running with zero delay.

BUG=568120, 569658
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1527893002

Cr-Commit-Position: refs/heads/master@{#365492}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index fb77e981..0b5a4af 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -570,6 +570,8 @@
     "test/begin_frame_source_test.h",
     "test/failure_output_surface.cc",
     "test/failure_output_surface.h",
+    "test/fake_channel_impl.cc",
+    "test/fake_channel_impl.h",
     "test/fake_content_layer_client.cc",
     "test/fake_content_layer_client.h",
     "test/fake_delegated_renderer_layer.cc",
@@ -891,6 +893,7 @@
     "trees/occlusion_tracker_unittest.cc",
     "trees/occlusion_unittest.cc",
     "trees/property_tree_unittest.cc",
+    "trees/proxy_impl_unittest.cc",
     "trees/threaded_channel_unittest.cc",
     "trees/tree_synchronizer_unittest.cc",