Hide "Skip" button on migration screen on Kevin.

To force migration on Kevin, we are removing "Skip" button from the migration
screen.
"Skip" should still be available in other boards.
Even on Kevin, "Skip" is still available when there is no enough storage to
start migration.

Bug: 852228
Test: Manually confirmed that Skip button is hidden on Kevin and visible on Eve.
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ibd5142db654a3797719feab134de0ea2352cc7dc
Reviewed-on: https://chromium-review.googlesource.com/1098870Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Naoki Fukino <fukino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567057}

chrome/browser/resources/chromeos/login/encryption_migration.html

@@ -56,7 +56,8 @@
         <template is="dom-if" if="[[!isResuming]]">
           <div class="bottom-buttons flex layout horizontal">
             <div class="flex"></div>
-            <oobe-text-button border on-tap="onSkip_">
+            <oobe-text-button border on-tap="onSkip_"
+                hidden="[[isSkipHidden_()]]">
               <div>$i18n{migrationButtonSkip}</div>
             </oobe-text-button>
             <oobe-text-button inverse on-tap="onUpgrade_"

chrome/browser/resources/chromeos/login/encryption_migration.js

@@ -153,6 +153,19 @@ Polymer({
     return !isEnoughBattery || isSkipped;
   },
 
+  /**
+   * Returns true if the 'Skip' button on the initial screen should be hidden.
+   * @return {boolean}
+   */
+  isSkipHidden_: function() {
+    // TODO(fukino): Instead of checking the board name here to behave
+    // differently, it's recommended to add a command-line flag to Chrome and
+    // make session_manager pass it based on a feature-based USE flag which is
+    // set in the appropriate board overlays.
+    // https://goo.gl/BbBkzg.
+    return this.i18n('migrationBoardName').startsWith('kevin');
+  },
+
   /**
    * Computes the label shown under progress bar.
    * @param {number} progress

chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.cc

@@ -367,6 +367,7 @@ void EncryptionMigrationScreenHandler::DeclareLocalizedValues(
                IDS_ENCRYPTION_MIGRATION_BUTTON_CONTINUE);
   builder->Add("migrationButtonSignIn", IDS_ENCRYPTION_MIGRATION_BUTTON_SIGNIN);
   builder->Add("migrationButtonReportAnIssue", IDS_REPORT_AN_ISSUE);
+  builder->Add("migrationBoardName", base::SysInfo::GetLsbReleaseBoard());
   builder->Add("gaiaLoading", IDS_LOGIN_GAIA_LOADING_MESSAGE);
 }