Add trace flag in cronet transport

doc/environment_variables.md

@@ -50,6 +50,7 @@ some configuration as environment variables that can be set.
     resolver and load balancing policy interaction
   - compression - traces compression operations
   - connectivity_state - traces connectivity state changes to channels
+  - cronet - traces state in the cronet transport engine
   - executor - traces grpc's internal thread pool ('the executor')
   - fd_trace - traces fd create(), shutdown() and close() calls for channel fds.
     Also traces epoll fd create()/close() calls in epollex polling engine

src/core/ext/transport/cronet/transport/cronet_transport.cc

@@ -29,6 +29,7 @@
 #include "src/core/ext/transport/chttp2/transport/bin_encoder.h"
 #include "src/core/ext/transport/chttp2/transport/incoming_metadata.h"
 #include "src/core/ext/transport/cronet/transport/cronet_transport.h"
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/gpr/host_port.h"
 #include "src/core/lib/gpr/string.h"
 #include "src/core/lib/gprpp/manual_constructor.h"
@@ -45,14 +46,12 @@
 #define GRPC_HEADER_SIZE_IN_BYTES 5
 #define GRPC_FLUSH_READ_SIZE 4096
 
+grpc_core::TraceFlag grpc_cronet_trace(false, "cronet");
 #define CRONET_LOG(...)                                    \
   do {                                                     \
-    if (grpc_cronet_trace) gpr_log(__VA_ARGS__); \
+    if (grpc_cronet_trace.enabled()) gpr_log(__VA_ARGS__); \
   } while (0)
 
-/* TODO (makdharma): Hook up into the wider tracing mechanism */
-int grpc_cronet_trace = 0;
-
 enum e_op_result {
   ACTION_TAKEN_WITH_CALLBACK,
   ACTION_TAKEN_NO_CALLBACK,