Background compilation work:

runtime/vm/code_generator.cc

Index: runtime/vm/code_generator.cc
diff --git a/runtime/vm/code_generator.cc b/runtime/vm/code_generator.cc
index 9b3eb295c83059e52210650f7fca07def7f3d33b..b3cb3bc4c0313f9ffe7796cb8da7c5f497c980da 100644
--- a/runtime/vm/code_generator.cc
+++ b/runtime/vm/code_generator.cc
@@ -59,6 +59,7 @@ DEFINE_FLAG(bool, trace_runtime_calls, false, "Trace runtime calls");
 DEFINE_FLAG(bool, trace_type_checks, false, "Trace runtime type checks.");
 
 DECLARE_FLAG(int, deoptimization_counter_threshold);
+DECLARE_FLAG(bool, enable_inlining_annotations);
 DECLARE_FLAG(bool, trace_compiler);
 DECLARE_FLAG(bool, warn_on_javascript_compatibility);
 DECLARE_FLAG(int, max_polymorphic_checks);
@@ -1487,6 +1488,9 @@ DEFINE_RUNTIME_ENTRY(OptimizeInvokedFunction, 1) {
 
   if (CanOptimizeFunction(function, thread)) {
     if (FLAG_background_compilation) {
+      if (FLAG_enable_inlining_annotations) {
+        FATAL("Cannot enable inlining annotations and background compilation");
+      }
       // Reduce the chance of triggering optimization while the function is
       // being optimized in the background. INT_MIN should ensure that it takes
       // long time to trigger optimization.