Fix memory leaking on ClosePage.
Fix memory leaking on ClosePage.

BUG=79367, 48791

The fonts was not cleared after unloading pages.

Test pdf: http://www.nasa.gov/pdf/750614main_NASA_FY_2014_Budget_Estimates-508.pdf
 For this file, we have ~5 fonts per page, which equal ~1 Mb per page.
 In this PDF we have 670 pages, as result after slow scrolling(reading) full document we have ~600 Mb fonts data in memory.

Memory usage of PDF Plugin:
 before this CL: ~660 Mb
 after this CL: ~100 Mb

This is last part of reverted CL:
 Original CL: https://codereview.chromium.org/2158023002
 Revert reason: BUG=647612
 Fix bug CL: https://codereview.chromium.org/2350193003
 Previous CL: https://codereview.chromium.org/2350243002

Review-Url: https://codereview.chromium.org/2351193002

DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium