Estimate content type from url when it's not available.

ui/file_manager/image_loader/request.js

Index: ui/file_manager/image_loader/request.js
diff --git a/ui/file_manager/image_loader/request.js b/ui/file_manager/image_loader/request.js
index 5e2e11162057a553087a95058448daa0c3073123..49fdd37e0f278cb7dbc470e56de837836f207b1b 100644
--- a/ui/file_manager/image_loader/request.js
+++ b/ui/file_manager/image_loader/request.js
@@ -228,6 +228,9 @@ Request.prototype.downloadOriginal_ = function(onSuccess, onFailure) {
 
   // Fetch the image via authorized XHR and parse it.
   var parseImage = function(contentType, blob) {
+    if (contentType)
+      this.contentType_ = contentType;
+
     this.image_.src = URL.createObjectURL(blob);
   }.bind(this);
 
@@ -245,6 +248,19 @@ function AuthorizedXHR() {
 }
 
 /**
+ * A map which is used to estimate content type from extension.
+ * @enum {string}
+ */
+AuthorizedXHR.ExtensionContentTypeMap = {
+  gif: 'image/gif',
+  png: 'image/png',
+  svg: 'image/svg',
+  bmp: 'image/bmp',
+  jpg: 'image/jpeg',
+  jpeg: 'image/jpeg'
+};
+
+/**
  * Aborts the current request (if running).
  */
 AuthorizedXHR.prototype.abort = function() {
@@ -268,6 +284,12 @@ AuthorizedXHR.prototype.load = function(url, onSuccess, onFailure) {
   // Do not call any callbacks when aborting.
   var onMaybeSuccess = /** @type {function(string, Blob)} */ (
       function(contentType, response) {
+        // When content type is not available, try to estimate it from url.
+        if (!contentType) {
+          contentType = AuthorizedXHR.ExtensionContentTypeMap[
+              this.extractExtension_(url)];
+        }
+
         if (!this.aborted_)
           onSuccess(contentType, response);
       }.bind(this));
@@ -318,6 +340,16 @@ AuthorizedXHR.prototype.load = function(url, onSuccess, onFailure) {
 };
 
 /**
+ * Extracts extension from url.
+ * @param {string} url Url.
+ * @return {string} Extracted extensiion, e.g. png.
+ */
+AuthorizedXHR.prototype.extractExtension_ = function(url) {
+  var result = (/\.([a-zA-Z]+)$/i).exec(url);
+  return result ? result[1] : '';
+};
+
+/**
  * Fetches data using authorized XmlHttpRequest with the provided OAuth2 token.
  * If the token is invalid, the request will fail.
  *