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

Index: pkg/dev_compiler/web/web_command.dart
diff --git a/pkg/dev_compiler/web/web_command.dart b/pkg/dev_compiler/web/web_command.dart
index 6ddda879637de5d7cc2df3fc4d0039a4bf0536f0..cac9be8f6055172a170215d4543ccf58f30dfe14 100644
--- a/pkg/dev_compiler/web/web_command.dart
+++ b/pkg/dev_compiler/web/web_command.dart
@@ -6,6 +6,7 @@ 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';
 
@@ -46,6 +47,7 @@ class JSMap<K, V> {
   external set(K k, V v);
   external JSIterator<K> keys();
   external JSIterator<V> values();
+  external int get size;
 }
 
 @JS('Array.from')
@@ -80,8 +82,23 @@ class WebCompileCommand extends Command {
   }
 
   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");
@@ -89,14 +106,21 @@ class WebCompileCommand extends Command {
       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.