Revert 111606 - Avoid references to untrusted.gypi in WebKit

Revert 111606 - Avoid references to untrusted.gypi in WebKit

Remove include of untrusted.gypi in normal ppapi gyp files
to prevent WebKit from depending on NaCl.

Refactor PPAPI gyp files to pull out source lists which are
shared between trusted and untrusted targets.

Fix scons hack which pulls list of sources from GYP so that
we can build with scons.

This CL should allow us to revert the DEPS change:
   http://trac.webkit.org/changeset/101011 on the webkit side 


BUG= none
TEST= Tools/Scripts/update-webkit --chromium
Review URL: http://codereview.chromium.org/8632023

TBR=noelallen@google.com
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=111608