Support all fast elements kinds in the major array operations.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 56ff07064f1b4c306810821fc07b561ee6a659a8..391381d01d24e540cfe5edc8df63c7e83fec1176 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1943,6 +1943,11 @@ void FixedArray::set_null_unchecked(Heap* heap, int index) {
 }
 
 
+double* FixedDoubleArray::data_start() {
+  return &READ_DOUBLE_FIELD(this, kHeaderSize);
+}
+
+
 Object** FixedArray::data_start() {
   return HeapObject::RawField(this, kHeaderSize);
 }
@@ -4788,6 +4793,11 @@ bool JSObject::HasFastHoleyElements() {
 }
 
 
+bool JSObject::HasFastElements() {
+  return IsFastElementsKind(GetElementsKind());
+}
+
+
 bool JSObject::HasDictionaryElements() {
   return GetElementsKind() == DICTIONARY_ELEMENTS;
 }