Reland: Add traits to ChainedTasks so we can prioritize accordingly.

The problem with mojo that lead to the revery has been fixed.

Original path: https://chromium-review.googlesource.com/c/chromium/src/+/1517707

Both usages count as bootstrap tasks which will be prioritized by a
subsequent patch.

(cherry picked from commit 8ed84293465fa4eba6a3416729c7a121ff706e96)

TBR: yfriedman@chromium.org
Bug: 863341, 974006
Change-Id: I95cae97d1b8e8d9ed5cdab3b8bd323b5c38d3026
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1617771
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Commit-Queue: Alex Clarke <alexclarke@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#666687}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1661311
Reviewed-by: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/branch-heads/3809@{#332}
Cr-Branched-From: d82dec1a818f378c464ba307ddd9c92133eac355-refs/heads/master@{#665002}

• chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/phone/StackLayoutBase.java[diff]
• chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java[diff]
• chrome/android/java/src/org/chromium/chrome/browser/init/ChainedTasks.java[diff]
• chrome/android/java/src/org/chromium/chrome/browser/init/ChromeBrowserInitializer.java[diff]
• chrome/android/java/src/org/chromium/chrome/browser/partnercustomizations/PartnerBrowserCustomizations.java[diff]
• chrome/android/javatests/src/org/chromium/chrome/browser/init/ChainedTasksTest.java[diff]
• chrome/android/javatests/src/org/chromium/chrome/browser/metrics/MainIntentBehaviorMetricsIntegrationTest.java[diff]
• chrome/android/javatests/src/org/chromium/chrome/browser/partnercustomizations/PartnerDisableBookmarksEditingUnitTest.java[diff]
• chrome/android/javatests/src/org/chromium/chrome/browser/partnercustomizations/PartnerDisableIncognitoModeUnitTest.java[diff]
• chrome/test/android/javatests/src/org/chromium/chrome/test/partnercustomizations/TestPartnerBrowserCustomizationsDelayedProvider.java[diff]