Add code comments to slow paths.

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
===================================================================
--- runtime/vm/intermediate_language_ia32.cc	(revision 15847)
+++ runtime/vm/intermediate_language_ia32.cc	(working copy)
@@ -1748,6 +1748,7 @@
       : instruction_(instruction) { }
 
   virtual void EmitNativeCode(FlowGraphCompiler* compiler) {
+    __ Comment("CheckStackOverflowSlowPath");
     __ Bind(entry_label());
     compiler->SaveLiveRegisters(instruction_->locs());
     compiler->GenerateCallRuntime(instruction_->token_pos(),
@@ -2084,6 +2085,7 @@
       : instruction_(instruction) { }
 
   virtual void EmitNativeCode(FlowGraphCompiler* compiler) {
+    __ Comment("BoxDoubleSlowPath");
     __ Bind(entry_label());
     const Class& double_class = compiler->double_class();
     const Code& stub =
@@ -2560,6 +2562,7 @@
       : instruction_(instruction) { }
 
   virtual void EmitNativeCode(FlowGraphCompiler* compiler) {
+    __ Comment("BoxIntegerSlowPath");
     __ Bind(entry_label());
     const Class& mint_class =
         Class::ZoneHandle(Isolate::Current()->object_store()->mint_class());