chrome.fileSystem API: Revise the use of Entry vs. FileEntry and allow
nullable Entry in chooseEntry callback.

In chooseEntry's callback, the first Entry arg in the callback turns out
to be passed null when the user cancels the chooseEntry Save File dialog.
The API docs confirm that the Entry passed to the callback can indeed be
optional and null.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=55035956
Add ECMA-402 definition of Date.toLocaleString
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=55041968