Bindings generation emits (more) correct null checking

Bindings generation emits (more) correct null checking
Re-apply "Throw exception on null pointers in raw toNative"

Adding in null checking to our toNative functions
(https://codereview.chromium.org/450053002/) exposed bugs
in our binding generation.  That patch was reverted, this
CL reapplies the patch, and adds in fixes to the binding
generation code so that we generate the correct toNative
functions.

Patch 1 is the original (reverted) patch from here:
https://codereview.chromium.org/450053002/

Patch 2 adds in fixes to the bindings code so that we generate the correct toNative calls.

BUG=http://dartbug.com/19948
R=vsm@google.com

Committed: https://src.chromium.org/viewvc/blink/branches/dart/dartium?view=rev&revision=180372

[vsm, 2014-08-15 10:28:25]

lgtm

[Leaf, 2014-08-15 16:17:58]

Committed patchset #2 manually as 180372 (presubmit successful).