Added a link to the new flake portal.

The URL to the new flake portal will be https://analysis.chromium.org/p/chromium/flake-portal
"Flake Portal" refers to the set of tools that Findit provides to deal with flakiness.

In Findit, the data in /p/chromium/flake-portal/flakes are flaky tests only, because successful and consistently failed tests are filtered out.
Besides, Findit has following features:
1) Flake Report: aggregation of flakiness data by crbug component.
2) Flake Analysis: find the culprit commit for a flaky test; verify flake fixes.
3) Flake bug management: auto-create flake bugs, comment on existing bugs filed by human, auto-merge flake bugs if the root cause is the same culprit, etc.

Also reworded the original "Flakiness Dashboard" to "Legacy Flakiness Dashboard".
It shows the full history of a specific test.
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=ChromeVoxLiveRegionsTest.LiveStatusOff

Bug: 934569
Change-Id: Ib05c43b67bf0f87307c135ca3f630200a7daf78f
Reviewed-on: https://chromium-review.googlesource.com/c/1482113
Commit-Queue: Shuotao Gao <stgao@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Erik Staab <estaab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636931}

infra/config/luci-milo-dev.cfg

@@ -77,10 +77,15 @@ headers: {
       url: "https://chromeperf.appspot.com/"
       alt: "Chrome perf dashboard"
     }
-    links: {
-      text: "flakiness"
+    links {
+      text: "flake-portal"
+      url: "https://analysis.chromium.org/p/chromium/flake-portal"
+      alt: "New flake portal"
+    }
+    links {
+      text: "legacy-flakiness"
       url: "https://test-results.appspot.com/dashboards/flakiness_dashboard.html"
-      alt: "Flakiness dashboard"
+      alt: "Legacy flakiness dashboard"
     }
   }
 

infra/config/luci-milo.cfg

@@ -76,9 +76,14 @@ headers {
       alt: "Chrome perf dashboard"
     }
     links {
-      text: "flakiness"
+      text: "flake-portal"
+      url: "https://analysis.chromium.org/p/chromium/flake-portal"
+      alt: "New flake portal"
+    }
+    links {
+      text: "legacy-flakiness"
       url: "https://test-results.appspot.com/dashboards/flakiness_dashboard.html"
-      alt: "Flakiness dashboard"
+      alt: "Legacy flakiness dashboard"
     }
   }
   links {