tracing: add OpenCensus agent exporter support to OpenCensus driver. (#8023)

Signed-off-by: Emil Mikulic <g-easy@users.noreply.github.com>

Mirrored from https://github.com/envoyproxy/envoy @ 816d6f14fd65329a8511351e74b385fafa3160a8

bazel/repository_locations.bzl

@@ -4,8 +4,8 @@ BAZEL_SKYLIB_SHA256 = "2ef429f5d7ce7111263289644d233707dba35e39696377ebab8b0bc70
 GOGOPROTO_RELEASE = "1.2.1"
 GOGOPROTO_SHA256 = "99e423905ba8921e86817607a5294ffeedb66fdd4a85efce5eb2848f715fdb3a"
 
-OPENCENSUS_PROTO_RELEASE = "0.2.1"
-OPENCENSUS_PROTO_SHA256 = "bfcefa6093fc2ecdf5c9effea86e6982d0d6f9a5178b17fcf73a62e0f3fb43d0"
+OPENCENSUS_PROTO_GIT_SHA = "5cec5ea58c3efa81fa808f2bd38ce182da9ee731"  # Jul 25, 2019
+OPENCENSUS_PROTO_SHA256 = "faeb93f293ff715b0cb530d273901c0e2e99277b9ed1c0a0326bca9ec5774ad2"
 
 PGV_GIT_SHA = "2feaabb13a5d697b80fcb938c0ce37b24c9381ee"  # Jul 26, 2018
 PGV_SHA256 = "ddefe3dcbb25d68a2e5dfea67d19c060959c2aecc782802bd4c1a5811d44dd45"
@@ -54,8 +54,8 @@ REPOSITORY_LOCATIONS = dict(
     ),
     opencensus_proto = dict(
         sha256 = OPENCENSUS_PROTO_SHA256,
-        strip_prefix = "opencensus-proto-" + OPENCENSUS_PROTO_RELEASE + "/src",
-        urls = ["https://github.com/census-instrumentation/opencensus-proto/archive/v" + OPENCENSUS_PROTO_RELEASE + ".tar.gz"],
+        strip_prefix = "opencensus-proto-" + OPENCENSUS_PROTO_GIT_SHA + "/src",
+        urls = ["https://github.com/census-instrumentation/opencensus-proto/archive/" + OPENCENSUS_PROTO_GIT_SHA + ".tar.gz"],
     ),
     kafka_source = dict(
         sha256 = KAFKA_SOURCE_SHA,

envoy/config/trace/v2/trace.proto

@@ -136,6 +136,14 @@ message OpenCensusConfig {
   // The URL to Zipkin, e.g. "http://127.0.0.1:9411/api/v2/spans"
   string zipkin_url = 6;
 
+  // Enables the OpenCensus Agent exporter if set to true. The address must also
+  // be set.
+  bool ocagent_exporter_enabled = 11;
+
+  // The address of the OpenCensus Agent, if its exporter is enabled, in gRPC
+  // format: https://github.com/grpc/grpc/blob/master/doc/naming.md
+  string ocagent_address = 12;
+
   reserved 7; // Formerly zipkin_service_name.
 
   enum TraceContext {