MD settings: Storage: Add DELETE button for deleting Drive offline files.

chrome/browser/resources/settings/device_page/storage.js

Index: chrome/browser/resources/settings/device_page/storage.js
diff --git a/chrome/browser/resources/settings/device_page/storage.js b/chrome/browser/resources/settings/device_page/storage.js
index 6649b8397e41b38e246e59b5070d050a1c6e71a6..4517f980cf045748b72848655802582f9e6703b7 100644
--- a/chrome/browser/resources/settings/device_page/storage.js
+++ b/chrome/browser/resources/settings/device_page/storage.js
@@ -55,6 +55,12 @@ Polymer({
       value: function() { return loadTimeData.getBoolean('isGuest'); }
     },
 
+    /** @private */
+    hasDriveCache_: {
+      type: Boolean,
+      value: false
+    },
+
     /** @private {settings.StorageSizeStat} */
     sizeStat_: Object,
   },
@@ -128,7 +134,8 @@ Polymer({
    */
   onDriveCacheTap_: function(e) {
     e.preventDefault();
-    this.$.storageDriveCache.open();
+    if (this.hasDriveCache_)
+      this.$.storageDriveCache.open();
   },
 
   /**
@@ -177,11 +184,14 @@ Polymer({
   /**
    * @param {string} size Formatted string representing the size of Offline
    *     files.
+   * @param {boolean} hasCache True if the device has at least one offline file.
    * @private
    */
-  handleDriveCacheSizeChanged_: function(size) {
-    if (this.driveEnabled_)
+  handleDriveCacheSizeChanged_: function(size, hasCache) {
+    if (this.driveEnabled_) {
       this.$$('#driveCacheSize').textContent = size;
+      this.hasDriveCache_ = hasCache;
+    }
   },
 
   /**