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This patch has the initial implementation of the VirtualKeyboard APIs
on Android. It uses the new virtualKeyboardPolicy that will let web
authors control the virtual keyboard behavior through JS by calling
virtual keyboard's show/hide APIs. In the next patch I'll implement
the geometrychange event that will let web authors control whether
to scroll the editable element into view by default or not and also
send the size of the virtual keyboard rectangle.
It is currently behind a runtime flag - VirtualKeyboard.
Explainers and Design Doc:
https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/VirtualKeyboardPolicy/explainer.md
https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/VirtualKeyboardAPI/explainer.md
https://docs.google.com/document/d/1I0LUNxK_gP5IaNQsbYN6gL6Zpm71XzduCKkublU5o5Q/edit?usp=sharing

Bug: 856269

Change-Id: I2424e016cad34e52f9c59503f1918f5c51e4bcd3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2386461
Commit-Queue: Anupam Snigdha <snianu@microsoft.com>
Reviewed-by: Changwan Ryu <changwan@chromium.org>
Reviewed-by: Mustaq Ahmed <mustaq@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804324}