
Improves IframeRelayTransport so that on IE, messages that would
exceed IE URL length limits are broken up into fragments and each
fragment is relayed separately. (The actual length limit, per
http://support.microsoft.com/kb/208427/EN-US, is 2083; we use 1800 as
our maximum fragment length, which should give enough headroom for
other elements of the URL in reasonable cases.) On receiving fragments,
the receiveMessage method will assemble them and deliver only when
fully assembled.

The implementation is not especially resilient if some fragments are
received by the recipient, but not others, but it seems hard to
insure against this sort of breakage. At any rate, the change as
presented for review unblocks me. :-)

R=mibuerge,agrieve
DELTA=111  (104 added, 3 deleted, 4 changed)


Revision created by MOE tool push_codebase.
MOE_MIGRATION=759


git-svn-id: 35241bd708fe29f1f6c7a4322d322e99ff93b95e@742 0b95b8e8-c90f-11de-9d4f-f947ee5921c8

johan/closure-library,johan/closure-library,johan/closure-library