Improve error handling in chrome.syncFileSystem
[chrome.syncFileSystem] Save local cache directoryEntry
[chrome.syncFileSystem] Make callback functions optional
[chrome.syncFileSystem] Override resolveLocalFileSystemURL to support syncfs
[chrome.syncFileSystem] Fixing lint errors
[chrome.syncFileSystem] Add reset method to clear cache
[chrome.identity] Update instructions for new developer console interface
[chrome.syncFileSystem] Update installation instructions