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When a AutofillHostMsg_QueryFormFieldAutofill message is sent from
an out-of-process iframe, its screen coordinates are relative to the
subframe's rect and not the top-level frame's viewport.

This CL exposes a facility in the content API to perform the necessary
transformation, particularly:
- it promotes GetView() from RenderFrameHostImpl to RenderFrameHost, so the RenderWidgetHostView becomes available to the embedder, and
- it promotes TransformPointToRootCoordSpace from RenderWidgetHostViewBase to RenderWidgetHostView, so that chrome/ or components/ code that directly receives coordinates from a renderer process can ensure they properly transformed

Finally, it causes the ContentAutofillDriver to use the exposed methods to transform received autofill popup coordinates in order for them to display in the correct position.

BUG=554119
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

Review URL: https://codereview.chromium.org/1526263003

Cr-Commit-Position: refs/heads/master@{#371519}