Add IR nodes needed for deferred loading.

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 646 matching lines @@
   Byte tag = 52;
   FunctionNode function;
 }
 
 type Let extends Expression {
   Byte tag = 53;
   VariableDeclaration variable;
   Expression body;
 }
 
+type LoadLibrary extends Expression {
+  Byte tag = 14;
+  LibraryReference library;
+}
+

[sra1, 2017/02/01 01:11:16]

Do you need at add DeferredLibary and the check here?

[asgerf, 2017/02/02 12:50:36]

Yep. Updated.

 abstract type Statement extends Node {}
 
 type InvalidStatement extends Statement {
   Byte tag = 60;
 }
 
 type ExpressionStatement extends Statement {
   Byte tag = 61;
   Expression expression;
 }
@@ skipping 240 matching lines @@
 
 /* enum BaseClassKind { None, Exact, Subclass, Subtype, } */
 
 type InferredValue {
   ClassReference baseClass; // May be NullReference if kind = None.
   Byte kind; // Index into BaseClassKind.
   Byte valueBits; // See lib/type_propagation/type_propagation.dart
 }
 
 ```