Fix setInitialScale() to take display density into account.

Reverted changes made to fix bug 4982074 (Book text display is limited
to about half the available screen.) The Books app sets initial scale to
100%, and since display density for Crespo is 1.5, initial scale was
actually being set to a smaller value in Device Independent Pixel units.

The correct fix is to take display density into account. This fixes bug
5477652: webview scale factor wrong on prime in reddit app.

Change-Id: Ie09172629add7fb28ca6b47d0fd8f6450c5df569