Fix the Google Hangouts extension icon loading issue.

When switch users, the 'FetchImage' function is called. However, if the
icon image has been loaded, the 'ChromeAppIconLoader::FetchImage'
function returns directly, and doesn't reset the icon for the delegate.
This might cause the blank icon issue for some extensions, e.g. the
Google Hangouts extension.

This CL modifies the function 'ChromeAppIconLoader::FetchImage'. If the
icon image has been loaded, call OnIconUpdated to set the icon for the
delegate.

BUG=1142226

Change-Id: I5d698844d72fbb71925d281cc11bc419e19f691e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2494409Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821587}

chrome/browser/extensions/chrome_app_icon_loader.cc

@@ -53,8 +53,12 @@ bool ChromeAppIconLoader::CanLoadImageForApp(const std::string& id) {
 }
 
 void ChromeAppIconLoader::FetchImage(const std::string& id) {
-  if (map_.find(id) != map_.end())
-    return;  // Already loading the image.
+  auto it = map_.find(id);
+  if (it != map_.end()) {
+    if (it->second && !it->second->image_skia().isNull())
+      OnIconUpdated(it->second.get());
+    return;  // Already loaded the image.
+  }
 
   const Extension* extension = GetExtensionByID(profile(), id);
   if (!extension)