FileManager: Fix type checking violations found with Closure v20190929.

 - Fix newly found JSC_HIDDEN_INTERFACE_PROPERTY_MISMATCH, as a result of
   the interface checking overhaul at [1]
 - Fix/suppress newly found JSC_CONSTANT_PROPERTY_REASSIGNED_VALUE errors.

This is in preparation of rolling a newer compiler version at a later CL.

[1] https://github.com/google/closure-compiler/commit/86acbd5e3ec78f08a1804df5f1efbea129d29c0e

Bug: 1012840
Change-Id: I8c356c9d2d3df03120f04614eafa555de488c8fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1850312
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704889}

ui/file_manager/base/js/mock_chrome.js

@@ -22,7 +22,7 @@ class MockCommandLinePrivate {
     }
 
     if (!chrome.commandLinePrivate) {
-      /** @suppress {checkTypes} */
+      /** @suppress {checkTypes, const} */
       chrome.commandLinePrivate = {};
     }
     chrome.commandLinePrivate.hasSwitch = (name, callback) => {
@@ -53,7 +53,7 @@ class MockChromeStorageAPI {
     window.chrome = window.chrome || {};
     /** @suppress {const} */
     window.chrome.runtime = window.chrome.runtime || {};  // For lastError.
-    /** @suppress {checkTypes} */
+    /** @suppress {checkTypes, const} */
     window.chrome.storage = {
       local: {
         get: this.get_.bind(this),

ui/file_manager/externs/background/import_history.js

@@ -78,7 +78,10 @@ importer.ImportHistory = class {
 /**
  * @enum {string} Import history changed event |state| values.
  */
-importer.ImportHistoryState = {};
+importer.ImportHistoryState = {
+  'COPIED': 'copied',
+  'IMPORTED': 'imported'
+};
 
 /**
  * Import history changed event (sent to ImportHistory.Observer's).

ui/file_manager/externs/entry_location.js

@@ -11,7 +11,7 @@ class EntryLocation {
   constructor() {
     /**
      * Volume information.
-     * @type {!VolumeInfo}
+     * @type {VolumeInfo}
      */
     this.volumeInfo;
 

ui/file_manager/externs/volume_manager.js

@@ -25,7 +25,7 @@ class VolumeManager {
    * Obtains a volume info containing the passed entry.
    * @param {!Entry|!FilesAppEntry} entry Entry on the volume to be
    *     returned. Can be fake.
-   * @return {VolumeInfo} The VolumeInfo instance or null if not found.
+   * @return {?VolumeInfo} The VolumeInfo instance or null if not found.
    */
   getVolumeInfo(entry) {}
 

ui/file_manager/file_manager/foreground/js/file_manager.js

@@ -19,9 +19,9 @@ class FileManager extends cr.EventTarget {
 
     /**
      * Volume manager.
-     * @private {?FilteredVolumeManager}
+     * @private {!FilteredVolumeManager}
      */
-    this.volumeManager_ = null;
+    this.volumeManager_;
 
     /** @private {?importer.HistoryLoader} */
     this.historyLoader_ = null;
@@ -438,7 +438,7 @@ class FileManager extends cr.EventTarget {
   }
 
   /**
-   * @return {FilteredVolumeManager}
+   * @return {!FilteredVolumeManager}
    */
   get volumeManager() {
     return this.volumeManager_;

ui/file_manager/file_manager/foreground/js/mock_thumbnail_loader.js

@@ -47,18 +47,18 @@ MockThumbnailLoader.testImageDataUrl = null;
 
 /**
  * Width of test image.
- * @private {number}
+ * @type {number}
  */
 MockThumbnailLoader.testImageWidth = 0;
 
 /**
  * Height of test image.
- * @private {number}
+ * @type {number}
  */
 MockThumbnailLoader.testImageHeight = 0;
 
 /**
  * Error urls.
- * @private {Array<string>}
+ * @type {Array<string>}
  */
 MockThumbnailLoader.errorUrls = [];

ui/file_manager/file_manager/foreground/js/ui/file_manager_ui.js

@@ -265,9 +265,9 @@ class FileManagerUI {
 
     /**
      * List container.
-     * @type {ListContainer}
+     * @type {!ListContainer}
      */
-    this.listContainer = null;
+    this.listContainer;
 
     /**
      * @type {!HTMLElement}