MacViews: Allow the BridgedNativeWidgetTest to focus its textfield
MacViews: Allow the BridgedNativeWidgetTest to focus its textfield

Some tests regressed in r316774 because the way edit commands were
dispatched in BridgedContentView changed from going directly to the
TextInputClient to instead go through the InputMethod.

r316774 included a check added to views::Textfield to ensure any
scheduled edit command had been processed before scheduling a new one.
Some tests failed that check: Because the textfield did not have focus,
the dispatch of the event that would commit the edit command was not
being received.

This CL ensures the textfield requests focus in the test.

Fixes (mac-only) views_unittests:
BridgedNativeWidgetTest.TextInput_MoveLeftRight
BridgedNativeWidgetTest.TextInput_DeleteBackward
BridgedNativeWidgetTest.TextInput_DeleteForward

BUG=454353

Review URL: https://codereview.chromium.org/941943003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#317715}

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