Protect against image conversion failure in mac::FaviconForTabContents().

chrome/browser/ui/cocoa/tab_contents/favicon_util.mm

Index: chrome/browser/ui/cocoa/tab_contents/favicon_util.mm
diff --git a/chrome/browser/ui/cocoa/tab_contents/favicon_util.mm b/chrome/browser/ui/cocoa/tab_contents/favicon_util.mm
index 390b8f9e2929755a60e0ad6cc67ac3d2b2b5fc13..3fcba52f3de804ede864461012e431a7d59222f2 100644
--- a/chrome/browser/ui/cocoa/tab_contents/favicon_util.mm
+++ b/chrome/browser/ui/cocoa/tab_contents/favicon_util.mm
@@ -19,8 +19,14 @@ NSImage* FaviconForTabContents(TabContents* contents) {
   // favicon.
   if (contents && contents->FaviconIsValid()) {
     CGColorSpaceRef color_space = base::mac::GetSystemColorSpace();
-    return gfx::SkBitmapToNSImageWithColorSpace(contents->GetFavicon(),
-                                                color_space);
+    NSImage* image =
+        gfx::SkBitmapToNSImageWithColorSpace(contents->GetFavicon(),
+                                             color_space);
+    // The |image| could be nil if the bitmap is null. In that case, fallback
+    // to the default image.
+    if (image) {
+      return image;
+    }
   }
 
   return app::mac::GetCachedImageWithName(@"nav.pdf");