- Preallocate non-named ArgumentsDescriptors with a small amount of parameters.

runtime/vm/dart_entry.h

Index: runtime/vm/dart_entry.h
===================================================================
--- runtime/vm/dart_entry.h	(revision 16642)
+++ runtime/vm/dart_entry.h	(working copy)
@@ -57,6 +57,9 @@
   // arguments. All arguments are positional.
   static RawArray* New(intptr_t count);
 
+  // Initialize the preallocated fixed length arguments descriptors cache.
+  static void InitOnce();
+
  private:
   // Absolute indexes into the array.
   enum {
@@ -72,13 +75,22 @@
     kNamedEntrySize,
   };
 
+  enum {
+    kCachedDescriptorCount = 32
+  };
+
   static intptr_t LengthFor(intptr_t count) {
     // Add 1 for the terminating null.
     return kFirstNamedEntryIndex + (kNamedEntrySize * count) + 1;
   }
 
+  static RawArray* NewNonCached(intptr_t count, bool canonicalize = true);
+
   const Array& array_;
 
+  // A cache of VM heap allocated arguments descriptors.
+  static RawArray* cached_args_descriptors_[kCachedDescriptorCount];
+
   DISALLOW_COPY_AND_ASSIGN(ArgumentsDescriptor);
 };