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Layout tests can choose a frame by name to navigate, using
testRunner.queueLoad(url, name).  This frame should be
found in the browser process rather than RenderFrameImpl.

This is useful cleanup in general, but also makes it possible
for layout tests to target OOPIFs.

TBR=dcheng,sky
BUG=477150
TEST=Layout tests continue to pass

Review URL: https://codereview.chromium.org/1104603002

Cr-Commit-Position: refs/heads/master@{#326928}