Turn off background compilation by default.

runtime/vm/flag_list.h

 // Copyright (c) 2012, 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_FLAG_LIST_H_
 #define VM_FLAG_LIST_H_
 
 // List of all flags in the VM.
 // Flags can be one of three categories:
 // * P roduct flags: Can be set in any of the deployment modes, including in
 //   production.
 // * D ebug flags: Can only be set in debug VMs, which also have assertions
 //   enabled.
 // * R elease flags: Generally available flags except when building product.
 // * pre C ompile flags: Generally available flags except when building product
 //   or precompiled runtime.
 //
 // Usage:
 //   P(name, type, default_value, comment)
 //   D(name, type, default_value, comment)
 //   R(name, product_value, type, default_value, comment)
 //   C(name, precompiled_value, product_value, type, default_value, comment)
 #define FLAG_LIST(P, R, D, C)                                                  \
 P(allow_absolute_addresses, bool, true,                                        \
   "Allow embedding absolute addresses in generated code.")                     \
 P(always_megamorphic_calls, bool, false,                                       \
   "Instance call always as megamorphic.")                                      \
-C(background_compilation, false, true, bool, true,                             \
+C(background_compilation, false, false, bool, false,                           \
   "Run optimizing compilation in background")                                  \
 C(collect_code, false, true, bool, true,                                       \
   "Attempt to GC infrequently used code.")                                     \
 P(collect_dynamic_function_names, bool, false,                                 \
   "Collects all dynamic function names to identify unique targets")            \
 R(dedup_instructions, true, bool, false,                                       \
   "Canonicalize instructions when precompiling.")                              \
 C(deoptimize_alot, false, false, bool, false,                                  \
   "Deoptimizes we are about to return to Dart code from native entries.")      \
 C(deoptimize_every, 0, 0, int, 0,                                              \
@@ skipping 101 matching lines @@
 P(verbose_gc, bool, false,                                                     \
   "Enables verbose GC.")                                                       \
 P(verbose_gc_hdr, int, 40,                                                     \
   "Print verbose GC header interval.")                                         \
 R(verify_after_gc, false, bool, false,                                         \
   "Enables heap verification after GC.")                                       \
 R(verify_before_gc, false, bool, false,                                        \
   "Enables heap verification before GC.")                                      \
 
 #endif  // VM_FLAG_LIST_H_