Move Kernel strings into the VM's heap.

pkg/kernel/binary.md

 This file describes the binary format of Dart Kernel.
 
 Notation
 --------
 Bitmasks are described with the syntax:
 ```scala
     Byte flags (flag1, flag2, ..., flagN)
 ```
 where 'flag<N>' is the N-th least significant bit,
 (so flag1 is the least significant bit).
@@ skipping 46 matching lines @@
 consists of the UTF-8 encoded string stretching from offset endOffset[N-1]
 (inclusive) to endOffset[N] (exclusive).
 
 ``` scala
 type StringTable {
   List<UInt> endOffsets;
   Byte[endOffsets.last] utf8Bytes;
 }
 
 type StringReference {
-  UInt index; // Index into the Program's .strings.
+  UInt index; // Index into the Program's strings.
 }
 
 type Source {
   List<Byte> utf8Bytes;
   // Line starts are delta-encoded (they are encoded as line lengths).  The list
   // [0, 10, 25, 32, 42] is encoded as [0, 10, 15, 7, 10].
   List<Uint> lineStarts;
 }
 
 type UriSource {
@@ skipping 877 matching lines @@
   Byte tag = 88;
 }
 
 type TypeParameter {
   // Note: there is no tag on TypeParameter
   StringReference name; // Cosmetic, may be empty, not unique.
   DartType bound; // 'dynamic' if no explicit bound was given.
 }
 
 ```