[fuzzing] Add ability for api-fuzzer to create inproc channels (#35277)

Closes #35277

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35277 from ctiller:inproc-fuzzing 853c11f144
PiperOrigin-RevId: 590420030

test/core/end2end/fuzzers/api_fuzzer.cc

@@ -40,6 +40,7 @@
 #include <grpc/support/string_util.h>
 
 #include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h"
+#include "src/core/ext/transport/inproc/inproc_transport.h"
 #include "src/core/lib/address_utils/parse_address.h"
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/event_engine/default_event_engine.h"
@@ -54,7 +55,6 @@
 #include "src/core/lib/iomgr/resolve_address.h"
 #include "src/core/lib/iomgr/resolved_address.h"
 #include "src/core/lib/resolver/endpoint_addresses.h"
-#include "src/core/lib/resource_quota/resource_quota.h"
 #include "src/libfuzzer/libfuzzer_macro.h"
 #include "test/core/end2end/data/ssl_test_data.h"
 #include "test/core/end2end/fuzzers/api_fuzzer.pb.h"
@@ -416,13 +416,17 @@ ApiFuzzer::Result ApiFuzzer::CreateChannel(
   fuzzing_env.resource_quota = resource_quota();
   ChannelArgs args = testing::CreateChannelArgsFromFuzzingConfiguration(
       create_channel.channel_args(), fuzzing_env);
-  grpc_channel_credentials* creds =
-      create_channel.has_channel_creds()
-          ? ReadChannelCreds(create_channel.channel_creds())
-          : grpc_insecure_credentials_create();
-  channel_ = grpc_channel_create(create_channel.target().c_str(), creds,
-                                 args.ToC().get());
-  grpc_channel_credentials_release(creds);
+  if (create_channel.inproc()) {
+    channel_ = grpc_inproc_channel_create(server_, args.ToC().get(), nullptr);
+  } else {
+    grpc_channel_credentials* creds =
+        create_channel.has_channel_creds()
+            ? ReadChannelCreds(create_channel.channel_creds())
+            : grpc_insecure_credentials_create();
+    channel_ = grpc_channel_create(create_channel.target().c_str(), creds,
+                                   args.ToC().get());
+    grpc_channel_credentials_release(creds);
+  }
   GPR_ASSERT(channel_ != nullptr);
   channel_force_delete_ = false;
   return Result::kComplete;

test/core/end2end/fuzzers/api_fuzzer.proto

@@ -94,6 +94,7 @@ message CreateChannel {
     string target = 1;
     grpc.testing.FuzzingChannelArgs channel_args = 2;
     ChannelCreds channel_creds = 3;
+    bool inproc = 4;
 }
 
 message Http2ServerPort {