Change Frame to store a Page instead of a FrameHost.

Change Frame to store a Page instead of a FrameHost.

Since all methods have already been removed off FrameHost, change Frame
to store a Page and remove the indirection caused from going through the
FrameHost. This is pre-work to remove FrameHost. LocalFrame and
RemoteFrame will be updated similarly in a follow-up patch.

BUG=688614

[sashab, 2017-03-20 04:58:02]

sashab@chromium.org changed reviewers:
+ joelhockey@chromium.org

[haraken, 2017-03-20 05:37:07]

LGTM

[sashab, 2017-03-20 05:45:02]

The CQ bit was checked by sashab@chromium.org

[commit-bot: I haz the power, 2017-03-20 05:45:10]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[joelhockey, 2017-03-20 06:35:48]

joelhockey@chromium.org changed reviewers:
+ haraken@chromium.org

[joelhockey, 2017-03-20 06:35:48]

lgtm

[commit-bot: I haz the power, 2017-03-20 07:31:40]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1489988702074940, "parent_rev":
"b8a53b39667bab5aa73c5526b33bfdb04ea5351b", "commit_rev":
"fb902e3e380be95b54d49d49c702dc1a20b11cdf"}

[commit-bot: I haz the power, 2017-03-20 07:36:07]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-03-20 07:36:08]

Prior attempt to commit was detected, but we were not able to check whether the
issue was successfully committed. Please check Git history manually and re-check
CQ or close this issue as needed.