Don't consider --profile-vm when collecting allocation samples; introduce a separate --profile-vm-al

runtime/vm/profiler.cc

 // Copyright (c) 2013, 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.
 
 #include "platform/address_sanitizer.h"
 #include "platform/memory_sanitizer.h"
 #include "platform/utils.h"
 
 #include "vm/allocation.h"
 #include "vm/atomic.h"
@@ skipping 1067 matching lines @@
 
   if (!GetAndValidateThreadStackBounds(thread, fp, sp, &stack_lower,
                                        &stack_upper)) {
     // Could not get stack boundary.
     return;
   }
 
   Sample* sample = SetupSample(thread, sample_buffer, os_thread->trace_id());
   sample->SetAllocationCid(cid);
 
-  if (FLAG_profile_vm) {
+  // TODO(flutter/flutter#10744): Enable native stack walker.
+  if (FLAG_profile_vm && false) {

[zra, 2017/06/15 20:50:21]

Should we add a separate flag for this instead that is turned off in the Flutter
engine?

Maybe --profile_allocation_vm or --profile_vm_allocation. Not sure what a good
name would be.

[rmacnak, 2017/07/11 18:17:18]

So even with good frame pointer, using the native stack walker doesn't produce
the traces we intended when introduce allocation tracing because the Dart code
is hidden behind too many C++ frames to show up in the profile. Removed the
reference to the frame pointers in Flutter Android bug and introduced a separate
flag as Zach suggests.

     ProfilerNativeStackWalker native_stack_walker(
         (isolate != NULL) ? isolate->main_port() : ILLEGAL_PORT, sample,
         sample_buffer, stack_lower, stack_upper, pc, fp, sp);
     native_stack_walker.walk();
   } else if (exited_dart_code) {
     ProfilerDartStackWalker dart_exit_stack_walker(
         thread, sample, sample_buffer, stack_lower, stack_upper, pc, fp, sp,
         exited_dart_code, true);
     dart_exit_stack_walker.walk();
   } else {
@@ skipping 514 matching lines @@
 
 
 ProcessedSampleBuffer::ProcessedSampleBuffer()
     : code_lookup_table_(new CodeLookupTable(Thread::Current())) {
   ASSERT(code_lookup_table_ != NULL);
 }
 
 #endif  // !PRODUCT
 
 }  // namespace dart