Add asserts to String::GetFlatContent.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 1dc170410951f7e01238815dae3b62340e6f6721..d5e28abf8d4b8bff57aad760dc6e3c192d7fedbb 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -6880,6 +6880,7 @@ bool String::LooksValid() {
 
 
 String::FlatContent String::GetFlatContent() {
+  ASSERT(!GetHeap()->allow_allocation(false));
   int length = this->length();
   StringShape shape(this);
   String* string = this;
@@ -7106,6 +7107,8 @@ void FlatStringReader::PostGarbageCollection() {
   if (str_ == NULL) return;
   Handle<String> str(str_);
   ASSERT(str->IsFlat());
+  AssertNoAllocation no_gc;
+  // This does not actually prevent the vector from being relocated later.
   String::FlatContent content = str->GetFlatContent();
   ASSERT(content.IsFlat());
   is_ascii_ = content.IsAscii();
@@ -7656,6 +7659,7 @@ bool String::IsUtf8EqualTo(Vector<const char> str) {
 bool String::IsOneByteEqualTo(Vector<const uint8_t> str) {
   int slen = length();
   if (str.length() != slen) return false;
+  AssertNoAllocation no_gc;
   FlatContent content = GetFlatContent();
   if (content.IsAscii()) {
     return CompareChars(content.ToOneByteVector().start(),
@@ -7671,6 +7675,7 @@ bool String::IsOneByteEqualTo(Vector<const uint8_t> str) {
 bool String::IsTwoByteEqualTo(Vector<const uc16> str) {
   int slen = length();
   if (str.length() != slen) return false;
+  AssertNoAllocation no_gc;
   FlatContent content = GetFlatContent();
   if (content.IsTwoByte()) {
     return CompareChars(content.ToUC16Vector().start(), str.start(), slen) == 0;