In that case, I don't think, it would be counted as eligible work experience as you started working when you were still a full-time student (in the eyes of CIC), so that isn't eligible W.E as per CIC CEC stream guidelines.
According to CIC guidelines given here:
http://www.cic.gc.ca/english/resources/tools/perm/econ/cec/work.asp
"Any period of employment when the applicant was engaged in full-time study will not be included in calculating the period of qualifying work experience (e.g., work experience gained through co-op work permits,
off-campus work permits while a full-time student and on-campus work permits). [R87.1(3)(a)]. Officers should verify the work permit information in GCMS."
However, any experience accumulated after you had applied for PGWP and are waiting for approval does count.
Link:
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1181&top=15
So basically, after you graduate, your current study permit authorizes you to work for 3 months; then if you apply for the PGWP before the end of that 3-month grace period, you are in implied status.
And in this period (the period after applying for PGWP and before getting approval) -
(1) your work experience is legal and authorized
(2) you are no longer a full-time student.