Collect the types used in is-checks in the resolver phase.

lib/compiler/implementation/resolver.dart

Index: lib/compiler/implementation/resolver.dart
diff --git a/lib/compiler/implementation/resolver.dart b/lib/compiler/implementation/resolver.dart
index d9fde2468d86e0429f93c1ff3365cc7208d162d2..743eb612c44d405e5c9dd8956ad7d2da7f7e405e 100644
--- a/lib/compiler/implementation/resolver.dart
+++ b/lib/compiler/implementation/resolver.dart
@@ -945,6 +945,7 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
   final Element enclosingElement;
   final TypeResolver typeResolver;
   bool inInstanceContext;
+  bool inCheckContext;
   Scope scope;
   ClassElement currentClass;
   bool typeRequired = false;
@@ -959,12 +960,12 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
       // fields.
       inInstanceContext = (element.isInstanceMember() && !element.isField())
           || element.isGenerativeConstructor(),
-      this.currentClass = element.isMember() ?
-                              element.getEnclosingClass() :
-                              null,
+      this.currentClass = element.isMember() ? element.getEnclosingClass()
+                                             : null,
       this.statementScope = new StatementScope(),
       typeResolver = new TypeResolver(compiler),
       scope = element.buildEnclosingScope(),
+      inCheckContext = compiler.enableTypeAssertions,
       super(compiler) {
   }
 
@@ -990,6 +991,14 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
     return element;
   }
 
+  doInCheckContext(action()) {
+    bool wasInCheckContext = inCheckContext;
+    inCheckContext = true;
+    var result = action();
+    inCheckContext = wasInCheckContext;
+    return result;
+  }
+
   inStaticContext(action()) {
     bool wasInstanceContext = inInstanceContext;
     inInstanceContext = false;
@@ -1030,7 +1039,12 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
 
   Element visitTypeAnnotation(TypeAnnotation node) {
     Type type = resolveTypeAnnotation(node);
-    if (type !== null) return type.element;
+    if (type !== null) {
+      if (inCheckContext) {
+        compiler.enqueuer.resolution.registerIsCheck(type);
+      }
+      return type.element;
+    }
     return null;
   }
 
@@ -1336,7 +1350,10 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
       String operatorString = node.selector.asOperator().source.stringValue;
       if (operatorString === 'is' || operatorString === 'as') {
         assert(node.arguments.tail.isEmpty());
-        resolveTypeTest(node.arguments.head);
+        Type type = resolveTypeTest(node.arguments.head);
+        if (type != null) {
+          compiler.enqueuer.resolution.registerIsCheck(type);
+        }
         resolvedArguments = true;
       }
     }
@@ -1595,9 +1612,13 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
 
   Type resolveTypeAnnotation(TypeAnnotation node) {
     Function report = typeRequired ? error : warning;
-    return typeResolver.resolveTypeAnnotation(node, inScope: scope,
-                                              onFailure: report,
-                                              whenResolved: useType);
+    Type type = typeResolver.resolveTypeAnnotation(node, inScope: scope,
+                                                   onFailure: report,
+                                                   whenResolved: useType);
+    if (compiler.enableTypeAssertions) {
+      compiler.enqueuer.resolution.registerIsCheck(type);
+    }
+    return type;
   }
 
   visitModifiers(Modifiers node) {
@@ -1848,8 +1869,16 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
         error(extra, MessageKind.EXTRA_CATCH_DECLARATION);
       }
     }
-    visitIn(node.type, blockScope);
-    visitIn(node.formals, blockScope);
+    if (node.type != null) {
+      doInCheckContext(() => visitIn(node.type, blockScope));
+      visitIn(node.formals, blockScope);
+    } else {
+      // The type annotation for the exception type is on the first formal.
+      doInCheckContext(() => visitIn(node.formals.nodes.head, blockScope));
+      if (!node.formals.nodes.tail.isEmpty()) {
+        visitIn(node.formals.nodes.tail.head, blockScope);
+      }
+    }
     visitIn(node.block, blockScope);
   }