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

src/arm/code-stubs-arm.cc

Index: src/arm/code-stubs-arm.cc
===================================================================
--- src/arm/code-stubs-arm.cc	(revision 9309)
+++ src/arm/code-stubs-arm.cc	(working copy)
@@ -3181,6 +3181,7 @@
   } else {
     __ vmov(r0, r1, d2);
   }
+  AllowExternalCallThatCantCauseGC scope(masm);
   switch (type_) {
     case TranscendentalCache::SIN:
       __ CallCFunction(ExternalReference::math_sin_double_function(isolate),
@@ -3334,12 +3335,23 @@
 
 
 bool CEntryStub::CompilingCallsToThisStubIsGCSafe() {
-  return !save_doubles_ && result_size_ == 1;
+  return (!save_doubles_ || ISOLATE->fp_stubs_generated()) &&
+          result_size_ == 1;
 }
 
 
 void CodeStub::GenerateStubsAheadOfTime() {
 }
+
+
+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(r0);
 }