Move some isolate state setup from C++ code to JumpToExceptionHandler stub

runtime/vm/stub_code.cc

Index: runtime/vm/stub_code.cc
diff --git a/runtime/vm/stub_code.cc b/runtime/vm/stub_code.cc
index 060fac92ad36d9008babe88186c66a5410daeba2..30987b2e518ef386fe585126869ffec98c340417 100644
--- a/runtime/vm/stub_code.cc
+++ b/runtime/vm/stub_code.cc
@@ -103,6 +103,13 @@ bool StubCode::InInvocationStubForIsolate(Isolate* isolate, uword pc) {
 }
 
 
+bool StubCode::InJumpToExceptionHandlerStub(uword pc) {
+  uword entry = StubCode::JumpToExceptionHandlerEntryPoint();
+  uword size = StubCode::JumpToExceptionHandlerSize();
+  return (pc >= entry) && (pc < (entry + size));
+}
+
+
 RawCode* StubCode::GetAllocationStubForClass(const Class& cls) {
   Isolate* isolate = Isolate::Current();
   const Error& error = Error::Handle(isolate, cls.EnsureIsFinalized(isolate));