Add filename to grit exception

This is helpful when debugging grd exceptions.

Change-Id: Ib78d6bf75bed82d98b6e8bdceff97a9c8fa03dd1
Reviewed-on: https://chromium-review.googlesource.com/c/1482131Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Mustafa Emre Acer <meacer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634526}

tools/grit/grit/grd_reader.py

@@ -88,7 +88,7 @@ class GrdContentHandler(xml.sax.handler.ContentHandler):
       partname = os.path.join(self.dir, partnode.GetInputPath())
       # Check the GRDP file exists.
       if not os.path.exists(partname):
-        raise exception.FileNotFound()
+        raise exception.FileNotFound(partname)
       # Exceptions propagate to the handler in grd_reader.Parse().
       oldsource = self.source
       try:
@@ -110,7 +110,8 @@ class GrdContentHandler(xml.sax.handler.ContentHandler):
         self.stack[-1].AppendContent(content)
 
   def ignorableWhitespace(self, whitespace):
-    # TODO(joi)  This is not supported by expat.  Should use a different XML parser?
+    # TODO(joi): This is not supported by expat. Should use a different XML
+    # parser?
     pass