[Cronet] Provide shim from deprecated cronet_c_for_grpc API to bidirectional_stream_c API.

components/cronet/ios/BUILD.gn

Index: components/cronet/ios/BUILD.gn
diff --git a/components/cronet/ios/BUILD.gn b/components/cronet/ios/BUILD.gn
index ba6ad852e3d9f9ced55f63f468a8bd1b95100b32..a449ceba8af166523b60b7f0b96fb8b4463c3fd8 100644
--- a/components/cronet/ios/BUILD.gn
+++ b/components/cronet/ios/BUILD.gn
@@ -53,6 +53,7 @@ source_set("cronet_sources") {
     "../url_request_context_config.h",
     "Cronet.h",
     "Cronet.mm",
+    "cronet_c_for_grpc.h",
     "cronet_environment.h",
     "cronet_environment.mm",
   ]
@@ -153,7 +154,10 @@ ios_framework_bundle("cronet_framework") {
     "//components/grpc_support",
   ]
 
-  public_headers = [ "Cronet.h" ]
+  public_headers = [
+    "Cronet.h",
+    "cronet_c_for_grpc.h",
+  ]
   public_headers += grpc_public_headers
 
   sources = [