Detect total switches to prevent type pollution by default cases.

sdk/lib/_internal/compiler/implementation/ssa/nodes.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart b/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
index 774ab84a4384117b534b3d3d3ba1c4ae3aeb6b0b..e8884405003b1322ab98dbf25ada8881c3b20169 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
@@ -1716,6 +1716,12 @@ class HSwitch extends HControlFlow {
    */
   HBasicBlock get defaultTarget => block.successors.last;
 
+  /**
+   * Set to true if we statically know that the case statements
+   * are exhaustive wrt the range of the expression.
+   */
+  bool isTotal = false;
+
   accept(HVisitor visitor) => visitor.visitSwitch(this);
 
   String toString() => "HSwitch cases = $inputs";