Reorganize ext tree

- filters live under filters
- lb_policy, resolver implementations (being part of client_channel) live under client_channel
diff --git a/src/core/ext/filters/client_channel/http_proxy.c b/src/core/ext/filters/client_channel/http_proxy.c
new file mode 100644
index 0000000..f8a2d06
--- /dev/null
+++ b/src/core/ext/filters/client_channel/http_proxy.c
@@ -0,0 +1,125 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/ext/filters/client_channel/http_proxy.h"
+
+#include <stdbool.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+
+#include "src/core/ext/filters/client_channel/http_connect_handshaker.h"
+#include "src/core/ext/filters/client_channel/proxy_mapper_registry.h"
+#include "src/core/ext/filters/client_channel/uri_parser.h"
+#include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/support/env.h"
+
+static char* grpc_get_http_proxy_server(grpc_exec_ctx* exec_ctx) {
+  char* uri_str = gpr_getenv("http_proxy");
+  if (uri_str == NULL) return NULL;
+  grpc_uri* uri =
+      grpc_uri_parse(exec_ctx, uri_str, false /* suppress_errors */);
+  char* proxy_name = NULL;
+  if (uri == NULL || uri->authority == NULL) {
+    gpr_log(GPR_ERROR, "cannot parse value of 'http_proxy' env var");
+    goto done;
+  }
+  if (strcmp(uri->scheme, "http") != 0) {
+    gpr_log(GPR_ERROR, "'%s' scheme not supported in proxy URI", uri->scheme);
+    goto done;
+  }
+  if (strchr(uri->authority, '@') != NULL) {
+    gpr_log(GPR_ERROR, "userinfo not supported in proxy URI");
+    goto done;
+  }
+  proxy_name = gpr_strdup(uri->authority);
+done:
+  gpr_free(uri_str);
+  grpc_uri_destroy(uri);
+  return proxy_name;
+}
+
+static bool proxy_mapper_map_name(grpc_exec_ctx* exec_ctx,
+                                  grpc_proxy_mapper* mapper,
+                                  const char* server_uri,
+                                  const grpc_channel_args* args,
+                                  char** name_to_resolve,
+                                  grpc_channel_args** new_args) {
+  *name_to_resolve = grpc_get_http_proxy_server(exec_ctx);
+  if (*name_to_resolve == NULL) return false;
+  grpc_uri* uri =
+      grpc_uri_parse(exec_ctx, server_uri, false /* suppress_errors */);
+  if (uri == NULL || uri->path[0] == '\0') {
+    gpr_log(GPR_ERROR,
+            "'http_proxy' environment variable set, but cannot "
+            "parse server URI '%s' -- not using proxy",
+            server_uri);
+    if (uri != NULL) grpc_uri_destroy(uri);
+    return false;
+  }
+  if (strcmp(uri->scheme, "unix") == 0) {
+    gpr_log(GPR_INFO, "not using proxy for Unix domain socket '%s'",
+            server_uri);
+    grpc_uri_destroy(uri);
+    return false;
+  }
+  grpc_arg new_arg;
+  new_arg.key = GRPC_ARG_HTTP_CONNECT_SERVER;
+  new_arg.type = GRPC_ARG_STRING;
+  new_arg.value.string = uri->path[0] == '/' ? uri->path + 1 : uri->path;
+  *new_args = grpc_channel_args_copy_and_add(args, &new_arg, 1);
+  grpc_uri_destroy(uri);
+  return true;
+}
+
+static bool proxy_mapper_map_address(grpc_exec_ctx* exec_ctx,
+                                     grpc_proxy_mapper* mapper,
+                                     const grpc_resolved_address* address,
+                                     const grpc_channel_args* args,
+                                     grpc_resolved_address** new_address,
+                                     grpc_channel_args** new_args) {
+  return false;
+}
+
+static void proxy_mapper_destroy(grpc_proxy_mapper* mapper) {}
+
+static const grpc_proxy_mapper_vtable proxy_mapper_vtable = {
+    proxy_mapper_map_name, proxy_mapper_map_address, proxy_mapper_destroy};
+
+static grpc_proxy_mapper proxy_mapper = {&proxy_mapper_vtable};
+
+void grpc_register_http_proxy_mapper() {
+  grpc_proxy_mapper_register(true /* at_start */, &proxy_mapper);
+}