Add a better bug reference for the fileBlob .bind() reasons

CL:2344335 used .bind(this, fileBlob) to handle the metadata callback,
or mime sniff callback, from the C++ for very good reasons. That's all
discussed issue 415792, comment 12 in particular. Change the crbug ref
comment in the code to point to that bug comment.

Bug: 1114622
Change-Id: Ic70a1afdeb0f84df08c6763231993ca8015fd6d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2350859Reviewed-by: Naoki Fukino <fukino@chromium.org>
Commit-Queue: Naoki Fukino <fukino@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Auto-Submit: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797110}

chrome/renderer/resources/extensions/file_manager_private_custom_bindings.js

@@ -129,7 +129,7 @@ apiBridge.registerCustomHook(function(bindingsAPI) {
 
     var onGetContentMimeType = function(blob, mimeType) {
       callback(mimeType ? mimeType : undefined);
-    }.bind(this, fileBlob);  // Bind a blob reference: crbug.com/415792.
+    }.bind(this, fileBlob);  // Bind a blob reference: crbug.com/415792#c12
 
     fileManagerPrivateInternal.getContentMimeType(uuid, onGetContentMimeType);
   });
@@ -145,7 +145,7 @@ apiBridge.registerCustomHook(function(bindingsAPI) {
 
     var onGetContentMetadata = function(blob, metadata) {
       callback(metadata ? metadata : undefined);
-    }.bind(this, fileBlob);  // Bind a blob reference: crbug.com/415792.
+    }.bind(this, fileBlob);  // Bind a blob reference: crbug.com/415792#c12
 
     fileManagerPrivateInternal.getContentMetadata(
         uuid, mimeType, type, onGetContentMetadata);