Reporting: Implement cache.

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index 091518f55924b7245c7941f08030e45131f36f32..da32c1decbdecc5e8ecb365d7f5407ebd30bb077 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -1388,6 +1388,8 @@ component("net") {
       "quic/quartc/quartc_stream.h",
       "quic/quartc/quartc_stream_interface.h",
       "quic/quartc/quartc_task_runner_interface.h",
+      "reporting/reporting_cache.cc",
+      "reporting/reporting_cache.h",
       "sdch/sdch_owner.cc",
       "sdch/sdch_owner.h",
       "socket/client_socket_factory.cc",
@@ -4581,6 +4583,9 @@ test("net_unittests") {
     "quic/test_tools/simulator/traffic_policer.h",
     "quic/test_tools/test_task_runner.cc",
     "quic/test_tools/test_task_runner.h",
+    "reporting/reporting_cache_unittest.cc",
+    "reporting/reporting_test_util.cc",
+    "reporting/reporting_test_util.h",
     "sdch/sdch_owner_unittest.cc",
     "socket/client_socket_pool_base_unittest.cc",
     "socket/mock_client_socket_pool_manager.cc",