[turbofan] Clarify comment about Parameter indexing.

[turbofan] Clarify comment about Parameter indexing.

This clarifies a comments in the AstGraphBuilder that has led to
confusion about what "parameter index" refers to. The off-by-one is
confusing and a terribly phrased comment doesn't make it any better.

R=rmcilroy@chromium.org,oth@chromium.org

Committed: https://crrev.com/b48e0c4a589ab6fa9f0d91012d437043e70f7622
Cr-Commit-Position: refs/heads/master@{#30616}

[oth, 2015-09-07 09:02:00]

On 2015/09/07 08:58:38, Michael Starzinger wrote:

Thanks Michael. LGTM.

[rmcilroy, 2015-09-07 09:10:32]

Ahh yes, it was the variable indexes which had the '-1', that explains my
confusion. Thanks!

lgtm.

[Michael Starzinger, 2015-09-07 09:12:01]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-09-07 09:12:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1329043002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1329043002/1

[commit-bot: I haz the power, 2015-09-07 09:37:06]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-07 09:37:20]

Patchset 1 (id:??) landed as
https://crrev.com/b48e0c4a589ab6fa9f0d91012d437043e70f7622
Cr-Commit-Position: refs/heads/master@{#30616}