[kernel] Debugging of switch statement

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 727 matching lines @@
 
 type SwitchStatement extends Statement {
   Byte tag = 71;
   Expression expression;
   List<SwitchCase> cases;
 }
 
 type SwitchCase {
   // Note: there is no tag on SwitchCase
   List<Expression> expressions;
+  FileOffset[expressions.length] expressionOffsets; // 1-to-1 with expressions.
   Byte isDefault; // 1 if default, 0 is not default.
   Statement body;
 }
 
 type ContinueSwitchStatement extends Statement {
   Byte tag = 72;
 
   // Reference to the Nth SwitchCase in scope.
   //
   // A SwitchCase is in scope everywhere within its enclosing switch,
@@ skipping 163 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
 }
 
 ```