Introduce FlexibleArrayBufferView and TypedFlexibleArrayBufferView

Source/bindings/core/v8/V8BindingMacros.h

Index: Source/bindings/core/v8/V8BindingMacros.h
diff --git a/Source/bindings/core/v8/V8BindingMacros.h b/Source/bindings/core/v8/V8BindingMacros.h
index 2377e9d0c1445e71a67a83ba53490c01fedf4887..9d68f90a667aa068d8a37935949567b05071ec0a 100644
--- a/Source/bindings/core/v8/V8BindingMacros.h
+++ b/Source/bindings/core/v8/V8BindingMacros.h
@@ -46,6 +46,14 @@ namespace blink {
     if (UNLIKELY(!var.prepare()))                  \
         return retVal;
 
+// Checks for a given v8::Value (value) whether it is an ArrayBufferView and
+// below a certain size limit. If below the limit, memory is allocated on the
+// stack to hold the actual payload. Keep the limit in sync with V8's
+// typed_array_max_size.
+#define allocateFlexibleArrayBufferViewStorage(value)                                       \
+    (value->IsArrayBufferView() && (value.As<v8::ArrayBufferView>()->ByteLength() <= 64) ?  \
+        alloca(value.As<v8::ArrayBufferView>()->ByteLength()) : nullptr)
+
 template <typename T>
 inline bool v8Call(v8::Maybe<T> maybe, T& outVariable)
 {