Reland of Change extension icon load errors to warnings

extensions/common/file_util.h

Index: extensions/common/file_util.h
diff --git a/extensions/common/file_util.h b/extensions/common/file_util.h
index 3fda56ad8f0d04e5e98548197d0e098c357fe557..609b27ce3605fb48618e11c8e536709664140178 100644
--- a/extensions/common/file_util.h
+++ b/extensions/common/file_util.h
@@ -71,6 +71,9 @@
     const base::FilePath& extension_root,
     const base::FilePath::CharType* manifest_filename,
     std::string* error);
+
+// Returns true if the given file path exists and is not zero-length.
+bool ValidateFilePath(const base::FilePath& path);
 
 // Returns true if the given extension object is valid and consistent.
 // May also append a series of warning messages to |warnings|, but they