PDF Viewer - PageUp/Down don't move pdf by page size in FitToPage mode

Currently when pdf is scaled to fit to page mode, both page down and
page up keys do not move pdf by page size. This is because both
the keys are not handled in HandleInputEvent().

This patch updates HandleInputEvent() to factor in key codes for
page up and page down to move pdf by page size in fit to page mode.
Similar to left and right arrow keys.

BUG=390599

Review URL: https://codereview.chromium.org/573523002

Cr-Commit-Position: refs/heads/master@{#300435}
1 file changed