Files.app: Clear the stored destination path on clear the drop target.

This patch prevents the mouse cursor icon from un-changing after the drop target is cleared when next drop target is not available.

BUG=226006
TEST=drag and drop works on Files.app

NOTRY=True
# for chromeos_chrome trybot passes.

Review URL: https://chromiumcodereview.appspot.com/13572006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@192807 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/file_manager/js/file_transfer_controller.js

@@ -477,8 +477,8 @@ FileTransferController.prototype = {
     if (this.dropTarget_ == domElement)
       return;
 
-    /** @type {string?} */
-    this.destinationPath_ = null;
+    // Remove the old drop target.
+    this.clearDropTarget_();
 
     // Add accept class if the domElement can accept the drag.
     if (isDirectory &&
@@ -487,9 +487,6 @@ FileTransferController.prototype = {
       this.destinationPath_ = destinationPath;
     }
 
-    // Remove the old drag target.
-    this.clearDropTarget_();
-
     // Set the new drop target.
     this.dropTarget_ = domElement;
 
@@ -514,6 +511,7 @@ FileTransferController.prototype = {
     if (this.dropTarget_ && this.dropTarget_.classList.contains('accepts'))
       this.dropTarget_.classList.remove('accepts');
     this.dropTarget_ = null;
+    this.destinationPath_ = null;
     if (this.navigateTimer_ !== undefined) {
       clearTimeout(this.navigateTimer_);
       this.navigateTimer_ = undefined;