Use a NSTextView to set expectations for BridgedNativeWidget text editing tests.
Use a NSTextView to set expectations for BridgedNativeWidget text editing tests.

This CL adds a NSTextView to BridgedNativeWidgetTest to set expectations for
text editing tests. Existing tests are refactored to use the same.

BUG=586985

Review-Url: https://codereview.chromium.org/1947933004
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#392875}

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