Remember all deopt reasons in ic_data, not just the last one.

runtime/vm/deopt_instructions.cc

Index: runtime/vm/deopt_instructions.cc
===================================================================
--- runtime/vm/deopt_instructions.cc	(revision 35415)
+++ runtime/vm/deopt_instructions.cc	(working copy)
@@ -44,12 +44,12 @@
       deferred_objects_(NULL) {
   object_table_ = code.object_table();
 
-  intptr_t deopt_reason = kDeoptUnknown;
+  DeoptReasonId deopt_reason = kDeoptUnknown;
   const DeoptInfo& deopt_info =
       DeoptInfo::Handle(code.GetDeoptInfoAtPc(frame->pc(), &deopt_reason));
   ASSERT(!deopt_info.IsNull());
   deopt_info_ = deopt_info.raw();
-  deopt_reason_ = static_cast<DeoptReasonId>(deopt_reason);
+  deopt_reason_ = deopt_reason;
 
   const Function& function = Function::Handle(code.function());
 
@@ -96,7 +96,7 @@
 
   if (FLAG_trace_deoptimization || FLAG_trace_deoptimization_verbose) {
     OS::PrintErr(
-        "Deoptimizing (reason %" Pd " '%s') at pc %#" Px " '%s' (count %d)\n",
+        "Deoptimizing (reason %d '%s') at pc %#" Px " '%s' (count %d)\n",
         deopt_reason,
         DeoptReasonToText(deopt_reason_),
         frame->pc(),
@@ -615,7 +615,7 @@
       ICData& ic_data = ICData::Handle();
       CodePatcher::GetInstanceCallAt(pc, code, &ic_data);
       if (!ic_data.IsNull()) {
-        ic_data.set_deopt_reason(deopt_context->deopt_reason());
+        ic_data.AddDeoptReason(deopt_context->deopt_reason());
       }
     } else if (deopt_context->deopt_reason() == kDeoptHoistedCheckClass) {
       // Prevent excessive deoptimization.