[Devtools] Network Downloading to use TTFB instead of headers received

Changes displayed timing info in network panel to use the requestStarted
(TTFB) instead of headersReceivedEnd. This will be more on par with what
HAR format uses. This is a minor change and most of the time
requestStarted and headersReceived is the same since the first packet
often has all the headers.

R=caseq
BUG=374557

Change-Id: I3e887b80f482843c0a98ae9ebc660bdfa611fe9c
Reviewed-on: https://chromium-review.googlesource.com/557466Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Blaise Bruer <allada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487339}

third_party/WebKit/Source/devtools/front_end/network/RequestTimingView.js

@@ -148,20 +148,23 @@ Network.RequestTimingView = class extends UI.VBox {
     if (issueTime < startTime)
       addRange(Network.RequestTimeRangeNames.Queueing, issueTime, startTime);
 
+    var responseReceived = (request.responseReceivedTime - startTime) * 1000;
     if (request.fetchedViaServiceWorker) {
       addOffsetRange(Network.RequestTimeRangeNames.Blocking, 0, timing.workerStart);
       addOffsetRange(Network.RequestTimeRangeNames.ServiceWorkerPreparation, timing.workerStart, timing.workerReady);
       addOffsetRange(Network.RequestTimeRangeNames.ServiceWorker, timing.workerReady, timing.sendEnd);
-      addOffsetRange(Network.RequestTimeRangeNames.Waiting, timing.sendEnd, timing.receiveHeadersEnd);
+      addOffsetRange(Network.RequestTimeRangeNames.Waiting, timing.sendEnd, responseReceived);
     } else if (!timing.pushStart) {
-      var blocking = firstPositive([timing.dnsStart, timing.connectStart, timing.sendStart]) || 0;
-      addOffsetRange(Network.RequestTimeRangeNames.Blocking, 0, blocking);
+      var blockingEnd = firstPositive([timing.dnsStart, timing.connectStart, timing.sendStart, responseReceived]) || 0;
+      addOffsetRange(Network.RequestTimeRangeNames.Blocking, 0, blockingEnd);
       addOffsetRange(Network.RequestTimeRangeNames.Proxy, timing.proxyStart, timing.proxyEnd);
       addOffsetRange(Network.RequestTimeRangeNames.DNS, timing.dnsStart, timing.dnsEnd);
       addOffsetRange(Network.RequestTimeRangeNames.Connecting, timing.connectStart, timing.connectEnd);
       addOffsetRange(Network.RequestTimeRangeNames.SSL, timing.sslStart, timing.sslEnd);
       addOffsetRange(Network.RequestTimeRangeNames.Sending, timing.sendStart, timing.sendEnd);
-      addOffsetRange(Network.RequestTimeRangeNames.Waiting, timing.sendEnd, timing.receiveHeadersEnd);
+      addOffsetRange(
+          Network.RequestTimeRangeNames.Waiting,
+          Math.max(timing.sendEnd, timing.connectEnd, timing.dnsEnd, timing.proxyEnd, blockingEnd), responseReceived);
     }
 
     if (request.endTime !== -1) {