Remove rootWindowRect from WebWidgetClient and move it to WebViewClient.

Since there's a single root window, even when multiple RenderWidgets are used to render the frame (with out-of-process iframes), it makes more sense to have the rootWindowRect implementation in the WebViewClient.

This is part of a refactor to split WebView/WebWidget.

BUG=419087

Review-Url: https://codereview.chromium.org/2148463002
Cr-Commit-Position: refs/heads/master@{#406336}
6 files changed