VM: Make use_osr an Isolate flag, similar to how we made use_field_guards.

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
diff --git a/runtime/vm/intermediate_language_ia32.cc b/runtime/vm/intermediate_language_ia32.cc
index e19bbf1b22c46e649583a56e0f91e720d337b95e..1f4f4196af2cf7bd02993b5efd8d54233b6ead47 100644
--- a/runtime/vm/intermediate_language_ia32.cc
+++ b/runtime/vm/intermediate_language_ia32.cc
@@ -2565,7 +2565,7 @@ class CheckStackOverflowSlowPath : public SlowPathCode {
       : instruction_(instruction) {}
 
   virtual void EmitNativeCode(FlowGraphCompiler* compiler) {
-    if (FLAG_use_osr && osr_entry_label()->IsLinked()) {
+    if (compiler->isolate()->use_osr() && osr_entry_label()->IsLinked()) {
       __ Comment("CheckStackOverflowSlowPathOsr");
       __ Bind(osr_entry_label());
       __ movl(Address(THR, Thread::stack_overflow_flags_offset()),
@@ -2583,7 +2583,8 @@ class CheckStackOverflowSlowPath : public SlowPathCode {
         instruction_->token_pos(), instruction_->deopt_id(),
         kStackOverflowRuntimeEntry, 0, instruction_->locs());
 
-    if (FLAG_use_osr && !compiler->is_optimizing() && instruction_->in_loop()) {
+    if (compiler->isolate()->use_osr() && !compiler->is_optimizing() &&
+        instruction_->in_loop()) {
       // In unoptimized code, record loop stack checks as possible OSR entries.
       compiler->AddCurrentDescriptor(RawPcDescriptors::kOsrEntry,
                                      instruction_->deopt_id(),
@@ -2595,7 +2596,7 @@ class CheckStackOverflowSlowPath : public SlowPathCode {
   }
 
   Label* osr_entry_label() {
-    ASSERT(FLAG_use_osr);
+    ASSERT(Isolate::Current()->use_osr());
     return &osr_entry_label_;
   }