1. Add flag --trace-api to trace API function invocation

runtime/vm/dart_api_impl.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_DART_API_IMPL_H_
 #define VM_DART_API_IMPL_H_
 
 #include "vm/allocation.h"
 #include "vm/native_arguments.h"
 #include "vm/object.h"
 
 namespace dart {
 
+DECLARE_FLAG(bool, trace_api);
+
 class ApiLocalScope;
 class ApiState;
 class FinalizablePersistentHandle;
 class LocalHandle;
 class PersistentHandle;
 
 const char* CanonicalFunction(const char* func);
 
 #define CURRENT_FUNC CanonicalFunction(__FUNCTION__)
 
+#if defined(DEBUG)
+#define TRACE_API_CALL(name)                                                   \
+  if (FLAG_trace_api) {                                                        \
+    OS::Print("Calling API func: %s\n", name);                                 \
+  }
+#else
+#define TRACE_API_CALL(name)
+#endif
+
+
 // Checks that the current isolate is not NULL.
 #define CHECK_ISOLATE(isolate)                                                 \
   do {                                                                         \
+    TRACE_API_CALL(CURRENT_FUNC);                                              \
     if ((isolate) == NULL) {                                                   \
       FATAL1("%s expects there to be a current isolate. Did you "              \
              "forget to call Dart_CreateIsolate or Dart_EnterIsolate?",        \
              CURRENT_FUNC);                                                    \
     }                                                                          \
   } while (0)
 
 // Checks that the current isolate is NULL.
 #define CHECK_NO_ISOLATE(isolate)                                              \
   do {                                                                         \
+    TRACE_API_CALL(CURRENT_FUNC);                                              \
     if ((isolate) != NULL) {                                                   \
       FATAL1("%s expects there to be no current isolate. Did you "             \
              "forget to call Dart_ExitIsolate?", CURRENT_FUNC);                \
     }                                                                          \
   } while (0)
 
 // Checks that the current isolate is not NULL and that it has an API scope.
 #define CHECK_ISOLATE_SCOPE(isolate)                                           \
   do {                                                                         \
     Isolate* tmp = (isolate);                                                  \
@@ skipping 201 matching lines @@
   if (isolate->no_callback_scope_depth() != 0) {                               \
     return reinterpret_cast<Dart_Handle>(Api::AcquiredError(isolate));         \
   }                                                                            \
 
 #define ASSERT_CALLBACK_STATE(isolate)                                         \
   ASSERT(isolate->no_callback_scope_depth() == 0)
 
 }  // namespace dart.
 
 #endif  // VM_DART_API_IMPL_H_