Check the available storage size before starting encryption migration.

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

Index: chrome/browser/resources/chromeos/login/encryption_migration.html
diff --git a/chrome/browser/resources/chromeos/login/encryption_migration.html b/chrome/browser/resources/chromeos/login/encryption_migration.html
index 6a76c3ee20f5386c41dee66535996e647d574bd6..7cb07c26f9ce6e8ba258c8ee45f0988fd738cc72 100644
--- a/chrome/browser/resources/chromeos/login/encryption_migration.html
+++ b/chrome/browser/resources/chromeos/login/encryption_migration.html
@@ -13,6 +13,11 @@
     <link rel="stylesheet" href="oobe_dialog_parameters.css">
     <template is="dom-if" if="[[isInitial_(uiState)]]">
       <oobe-dialog tabindex="0" has-buttons>
+        <p>Checking the system...</p>
+      </oobe-dialog>
+    </template>
+    <template is="dom-if" if="[[isReady_(uiState)]]">
+      <oobe-dialog tabindex="0" has-buttons>
         <div class="header">
           <h1 class="title">Your file system needs upgrade</h1>
           <div class="subtitle">
@@ -71,5 +76,20 @@
         </div>
       </oobe-dialog>
     </template>
+    <template is="dom-if" if="[[isNotEnoughSpace_(uiState)]]">

[fukino, 2017/04/10 12:08:50]

This screen's design is still temporary.
I'll update these screens to match the latest mock and make them
internationalized in a separate patch.

[xiyuan, 2017/04/10 17:24:55]

Acknowledged.

+      <oobe-dialog tabindex="0" has-buttons>
+        <div class="header">
+          <h1 class="title">Not enough storage for update</h1>
+          <div class="subtitle">
+            Please free up some space on your device and sign in again.
+          </div>
+        </div>
+        <div class="bottom-buttons flex layout horizontal">
+          <div class="flex"></div>
+          <oobe-text-button inverse on-tap="onSkip_">Continue
+          </oobe-text-button>
+        </div>
+      </oobe-dialog>
+    </template>
   </template>
 </dom-module>