Update known crashes....

Update known crashes.

Update crash signature: Crash in HTMLFormControlElement (74545)
Add new crash signature: Crash in WTF::StringImpl::createUninitialized (74796)

Found http://build.chromium.org/p/chromium/builders/Win%20Reliability/builds/2422/steps/reliability%3A%20partial%20result%20of%20current%20build/logs/stdio
These weren't found in next build.

BUG=74545, 74796
TEST=none
TBR=huanr


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=76732

[huanr, 2011-03-03 16:55:53]

LGTM