Make the MediaRouterDialogDelegate set initial dialog size in OSX

chrome/browser/ui/cocoa/constrained_window/constrained_window_web_dialog_sheet.mm

Index: chrome/browser/ui/cocoa/constrained_window/constrained_window_web_dialog_sheet.mm
diff --git a/chrome/browser/ui/cocoa/constrained_window/constrained_window_web_dialog_sheet.mm b/chrome/browser/ui/cocoa/constrained_window/constrained_window_web_dialog_sheet.mm
index 775ae154665490be79c47801ddf24210e1f13479..9bd73cf17d8034ecb1b89693874871ce40ca4b17 100644
--- a/chrome/browser/ui/cocoa/constrained_window/constrained_window_web_dialog_sheet.mm
+++ b/chrome/browser/ui/cocoa/constrained_window/constrained_window_web_dialog_sheet.mm
@@ -20,13 +20,13 @@
 
 - (void)updateSheetPosition {
   if (web_dialog_delegate_) {
-    gfx::Size size;
+    // If the dialog has autoresizing enabled and |current_size_| has been set,
+    // GetDialogSize() doesn't modify |size|.
+    gfx::Size size(current_size_.width, current_size_.height);
     web_dialog_delegate_->GetDialogSize(&size);
+    DCHECK(!size.IsEmpty());
 
-    // If the dialog has autoresizing enabled, |size| will be empty. Use the
-    // last known dialog size.
-    NSSize content_size = size.IsEmpty() ? current_size_ :
-        NSMakeSize(size.width(), size.height());
+    NSSize content_size = NSMakeSize(size.width(), size.height());
     [customWindow_ setContentSize:content_size];
   }
   [super updateSheetPosition];