Updated protobuf library to 2.5.0.

Change-Id: Ief9d57c13ae876bf431a0149c751874db86f6f33
Revert "Add a custom serializer for LinkedHashSet."

This reverts commit c8c4477e022bafeb3a61019ba87e3eb9ae58f57b.

Change-Id: I14ce7fff5ac450c9255f57aa95f8333b9080f660
blacklist all globals in each browser

Before we weren't being comprehensive about this and just blacklisting
names we got from Closure and other places. Instead, let's use a script
to get all the globals in a browser and blacklist them whether we think
they're likely to be used or not.

This only includes Firefox and Chrome to start; please run globals.html
in whatever browsers you have and contribute more globals files.

(We probably need to do something else to make it less likely that there
will be a conflict with a browser or extension we don't know about at
the time of release, but that's out of scope for this patch.)

Change-Id: Ib526b006a30990a4f29c19b1011472278813ed18
Review-Link: https://gwt-review.googlesource.com/#/c/5241/
add ie9 globals to blacklist

Also, add doctype to globals.html

Change-Id: I316133d15a35c754f8899fa34b154c4818153cf3
Merge from master