Remove line that crashes image_decoding.tough_decoding_cases

image_decoding.py was calling PageMeasurementResults.Add with a value
of the wrong type (a string instead of a scalar type). This was
crashing when the type was checked.

Note: I am not sure why this path is being followed in 
this test, but the code on this path was clearly broken.

NOTRY=true
TBR=tonyg@chromium.org
BUG=338813

Review URL: https://codereview.chromium.org/146283005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249399 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249399