Save more memory by compacting LocalVarDescriptors

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
===================================================================
--- runtime/vm/raw_object.h	(revision 40226)
+++ runtime/vm/raw_object.h	(working copy)
@@ -1097,12 +1097,28 @@
 
  private:
   RAW_HEAP_OBJECT_IMPLEMENTATION(LocalVarDescriptors);
-  RawArray* names_;  // Array of [length_] variable names.
-  int32_t length_;  // Number of descriptors.
+  int32_t num_entries_;  // Number of descriptors.
 
-  // Variable info with [length_] entries.
-  VarInfo* data() { OPEN_ARRAY_START(VarInfo, int32_t); }
+  RawObject** from() {
+    return reinterpret_cast<RawObject**>(&ptr()->names()[0]);
+  }
+  RawString** names() {
+    // Array of [num_entries_] variable names.
+    OPEN_ARRAY_START(RawString*, RawString*);
+  }
+  RawString** nameAddrAt(intptr_t i) {
+    return &(ptr()->names()[i]);
+  }
 
+  RawObject** to(intptr_t num_entries) {
+    return reinterpret_cast<RawObject**>(nameAddrAt(num_entries - 1));
+  }
+
+  // Variable info with [num_entries_] entries.
+  VarInfo* data() {
+    return reinterpret_cast<VarInfo*>(nameAddrAt(ptr()->num_entries_));
+  }
+
   friend class Object;
 };