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This change forwards navigator.requestKeyLock() and navigator.cancelKeyLock()
functions to the RenderFrameHostImpl.

System-Keyboard-Lock is a feature to detect the key presses which usually cannot
be received by the browser, and send them to the web page. It contains various
components to achieve the goal. This change is one of them, which receives
JavaScript (or Web Platform API in the design doc) function calls and forwards
them into RenderFrameHost. For detail, please refer to the design doc at,
https://docs.google.com/document/d/1T9gJHYdA1VGZ6QHQeOu0hOacWWWJ7yNEt1VDbLju4bs/edit#heading=h.cgwemqs2j4ta

W3C Working Draft: https://garykac.github.io/system-keyboard-lock/
Intent to implement: https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/9pauQUAvrcw/lfbG7eunCAAJ

BUG=680809
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2805763004
Cr-Commit-Position: refs/heads/master@{#468158}