Change FrameTreeNode id from int64 to int.
The FrameTreeNode class has a browser-side and globally unique id. we need id with less bits, for example in extension APIs code exporting those ids to JavaScript.

BUG=477770

TBR=sky

Review URL: https://codereview.chromium.org/1093923003

Cr-Commit-Position: refs/heads/master@{#327476}
27 files changed