build: Change namespace of chromium_url.

[jamessynge]

Rename namespace url to chromium_url. Avoids link-time collisions
in binaries which link in Envoy and the original chromium URL
library.

Fix format of chromium_url/README.md.

Signed-off-by: James Synge jamessynge@google.com

[jamessynge]

Several currently open PRs have the same test failure during the coverage run, so I'm guessing that the test itself is flaky

[ RUN      ] SslIpVersionsClientType/GrpcSslClientIntegrationTest.BasicSslRequestWithClientCert/IPv4_EnvoyGrpc
unknown file: Failure

Unexpected mock function call - returning directly.
    Function call: setTag(@0x1a969cc0 "grpc.status_code", @0x7ffeda5903d0 "14")
Google Mock tried the following 2 expectations, but none matched:

./test/common/grpc/grpc_client_integration_test_harness.h:352: tried expectation #0: EXPECT_CALL(*request->child_span_, setTag(Tracing::Tags::get().UpstreamCluster, fake_cluster_name_))...
  Expected arg #0: is equal to "upstream_cluster"
           Actual: "grpc.status_code"
  Expected arg #1: is equal to "fake_cluster"
           Actual: "14"
         Expected: to be called once
           Actual: called once - saturated and active
./test/common/grpc/grpc_client_integration_test_harness.h:354: tried expectation #1: EXPECT_CALL(*request->child_span_, setTag(Tracing::Tags::get().Component, Tracing::Tags::get().Proxy))...
  Expected arg #0: is equal to "component"
           Actual: "grpc.status_code"
  Expected arg #1: is equal to "proxy"
           Actual: "14"
         Expected: to be called once
           Actual: called once - saturated and active
unknown file: Failure
...

[htuch]

Thanks!