Speed up tests by not type-checking lib.d.ts unless the test asks for that.

src/compiler/checker.ts

@@ -11368,6 +11368,12 @@ module ts {
         function checkSourceFileWorker(node: SourceFile) {
             let links = getNodeLinks(node);
             if (!(links.flags & NodeCheckFlags.TypeChecked)) {
+                links.flags |= NodeCheckFlags.TypeChecked;
+
+                if (node.isDefaultLib && compilerOptions.skipDefaultLibCheck) {
+                    return;
+                }
+
                 // Grammar checking
                 checkGrammarSourceFile(node);
 
@@ -11399,8 +11405,6 @@ module ts {
                 if (emitParam) {
                     links.flags |= NodeCheckFlags.EmitParam;
                 }
-
-                links.flags |= NodeCheckFlags.TypeChecked;
             }
         }
 

src/compiler/program.ts

@@ -391,6 +391,7 @@ module ts {
                         processImportedModules(file, basePath);
                     }
                     if (isDefaultLib) {
+                        file.isDefaultLib = true;
                         files.unshift(file);
                     }
                     else {

src/compiler/types.ts

@@ -1143,7 +1143,8 @@ module ts {
 
         // The first node that causes this file to be an external module
         /* @internal */ externalModuleIndicator: Node;
-        
+
+        /* @internal */ isDefaultLib: boolean;
         /* @internal */ identifiers: Map<string>;
         /* @internal */ nodeCount: number;
         /* @internal */ identifierCount: number;
@@ -1823,6 +1824,7 @@ module ts {
         experimentalDecorators?: boolean;
         emitDecoratorMetadata?: boolean;
         /* @internal */ stripInternal?: boolean;
+        /* @internal */ skipDefaultLibCheck?: boolean;
         [option: string]: string | number | boolean;
     }