🔍 PromoDialog tests

Add a bunch of basic tests for the PromoDialog/PromoDialogLayout
that confirm that elements appear when they should, and that
clicking on them triggers the right events.

BUG=712836,712833

Review-Url: https://codereview.chromium.org/2842943002
Cr-Commit-Position: refs/heads/master@{#467590}

chrome/android/java_sources.gni

@@ -1613,6 +1613,7 @@ chrome_test_java_sources = [
   "javatests/src/org/chromium/chrome/browser/webapps/WebApkIntegrationTest.java",
   "javatests/src/org/chromium/chrome/browser/widget/DualControlLayoutTest.java",
   "javatests/src/org/chromium/chrome/browser/widget/OverviewListLayoutTest.java",
+  "javatests/src/org/chromium/chrome/browser/widget/PromoDialogTest.java",
   "javatests/src/org/chromium/chrome/browser/widget/RoundedIconGeneratorTest.java",
   "javatests/src/org/chromium/chrome/browser/widget/ToolbarProgressBarTest.java",
   "javatests/src/org/chromium/chrome/browser/widget/bottomsheet/BottomSheetObserverTest.java",