Fix asserts and GC unsafeness in stub generation, bug=1689.

src/ia32/code-stubs-ia32.cc

Index: src/ia32/code-stubs-ia32.cc
===================================================================
--- src/ia32/code-stubs-ia32.cc	(revision 9309)
+++ src/ia32/code-stubs-ia32.cc	(working copy)
@@ -4293,7 +4293,8 @@
 
 
 bool CEntryStub::CompilingCallsToThisStubIsGCSafe() {
-  return !save_doubles_ && result_size_ == 1;
+  return (!save_doubles_ || ISOLATE->fp_stubs_generated()) &&
+          result_size_ == 1;
 }
 
 
@@ -4301,6 +4302,14 @@
 }
 
 
+void CodeStub::GenerateFPStubs() {
+  CEntryStub save_doubles(1);
+  save_doubles.SaveDoubles();
+  Handle<Code> code = save_doubles.GetCode();
+  code->GetIsolate()->set_fp_stubs_generated(true);
+}
+
+
 void CEntryStub::GenerateThrowTOS(MacroAssembler* masm) {
   __ Throw(eax);
 }