Add progress events for loading DDC summaries to make it clear to users whether loading a DDC appli…

pkg/dev_compiler/web/web_command.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 @JS()
 library dev_compiler.web.web_command;
 
 import 'dart:async';
 import 'dart:convert';
+import 'dart:math' as math;
 import 'dart:html' show HttpRequest;
 import 'dart:typed_data';
 
 import 'package:analyzer/dart/element/element.dart'
     show
         LibraryElement,
         ImportElement,
         ShowElementCombinator,
         HideElementCombinator;
 import 'package:analyzer/file_system/file_system.dart' show ResourceUriResolver;
@@ skipping 20 matching lines @@
 @JS()
 @anonymous
 class JSIterator<V> {}
 
 @JS('Map')
 class JSMap<K, V> {
   external V get(K v);
   external set(K k, V v);
   external JSIterator<K> keys();
   external JSIterator<V> values();
+  external int get size;
 }
 
 @JS('Array.from')
 external List<V> iteratorToList<V>(JSIterator<V> iterator);
 
 @JS()
 @anonymous
 class CompileResult {
   external factory CompileResult(
       {String code, List<String> errors, bool isValid});
@@ skipping 14 matching lines @@
     CompilerOptions.addArguments(argParser);
     AnalyzerOptions.addArguments(argParser);
   }
 
   @override
   Function run() {
     return requestSummaries;
   }
 
   Future<Null> requestSummaries(String sdkUrl, JSMap<String, String> summaryMap,
-      Function onCompileReady, Function onError) async {
+      Function onCompileReady, Function onError, Function onProgress) async {
     var sdkRequest;
+    var progress = 0;
+    int lastReported = 0;
+    // Add 1 to the count for the SDK summary.
+    var total = summaryMap.size + 1;
+    // No need to report after every  summary is loaded. Posting about 100
+    // progress updates should be more than sufficient for users to understand
+    // how long loading will take.
+    num progressDelta = math.max(total / 100, 1);
+    num nextProgressToReport = 0;
+    maybeReportProgress() {
+      if (nextProgressToReport > progress && progress != total) return;
+      nextProgressToReport += progressDelta;
+      if (onProgress != null) onProgress(progress, total);
+    }
+
     try {
       sdkRequest = await HttpRequest.request(sdkUrl,
           responseType: "arraybuffer", mimeType: "application/octet-stream");
     } catch (error) {
       onError('Dart sdk summaries failed to load: $error. url: $sdkUrl');
       return null;
     }
+    progress++;
+    maybeReportProgress();
 
     var sdkBytes = (sdkRequest.response as ByteBuffer).asUint8List();
 
     // Map summary URLs to HttpRequests.
-    var summaryRequests = iteratorToList(summaryMap.values())
-        .map((String summaryUrl) => HttpRequest.request(summaryUrl,
-            responseType: "arraybuffer", mimeType: "application/octet-stream"))
-        .toList();
+
+    var summaryRequests =
+        iteratorToList(summaryMap.values()).map((String summaryUrl) async {
+      var ret = await HttpRequest.request(summaryUrl,

[Alan Knight, 2017/05/13 00:22:41]

Style guide frowns on abbreviations and non-meaningful names :-)  Can't you just
call it request?

+          responseType: "arraybuffer", mimeType: "application/octet-stream");
+      progress++;
+      maybeReportProgress();
+      return ret;
+    }).toList();
     try {
       var summaryResponses = await Future.wait(summaryRequests);
       // Map summary responses to summary bytes.
       List<List<int>> summaryBytes = summaryResponses
           .map((response) => (response.response as ByteBuffer).asUint8List())
           .toList();
       onCompileReady(setUpCompile(
           sdkBytes, summaryBytes, iteratorToList(summaryMap.keys())));
     } catch (error) {
       onError('Summaries failed to load: $error');
@@ skipping 190 matching lines @@
   if (source is InSummarySource) {
     return source.summaryPath.substring(1).replaceAll('.api.ds', '');
   }
   return source.toString().substring(1).replaceAll('.dart', '');
 }
 
 /// Thrown when the input source code has errors.
 class CompileErrorException implements Exception {
   toString() => '\nPlease fix all errors before compiling (warnings are okay).';
 }