Fix handling of Unicode BOMs in JSONReader.

Because |char| is signed, the upper bits of the BOM bytes were getting 
interpreted as the sign bit. Cast to |uint8| to preserve them for proper
comparison.

BUG=119975
TEST=Try to install the Gmail extension. Do not get JSON error when unpacking.

Review URL: http://codereview.chromium.org/9860035

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@129373 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed