Make --trace-natives respect the isolate filter.

runtime/vm/native_entry.h

Index: runtime/vm/native_entry.h
diff --git a/runtime/vm/native_entry.h b/runtime/vm/native_entry.h
index 187472f4a6372f4d1e2e448cb3cc60a582f3c3ce..5f6984e794e16848926e02682e96852ef37e1d19 100644
--- a/runtime/vm/native_entry.h
+++ b/runtime/vm/native_entry.h
@@ -11,6 +11,7 @@
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/exceptions.h"
+#include "vm/log.h"
 #include "vm/native_arguments.h"
 #include "vm/verifier.h"
 
@@ -36,6 +37,16 @@ class String;
 
 typedef void (*NativeFunction)(NativeArguments* arguments);
 
+#ifndef PRODUCT
+#define TRACE_NATIVE_CALL(format, name)                                        \
+  if (FLAG_trace_natives) {                                                    \
+    THR_Print("Calling native: " format "\n", name);                           \
+  }
+#else
+#define TRACE_NATIVE_CALL(format, name)                                        \
+  do {                                                                         \
+  } while (0)
+#endif
 
 #define NATIVE_ENTRY_FUNCTION(name) BootstrapNatives::DN_##name