DevTools: use installDragHandle to pan/rotate in Layers3DView

We used to use hand-crafter mouse-up/move/down event processing to control
layer 3d view pan/rotate which caused annoying text selection when mouse was
moved out of original view. Let's use WebInspector.installDragHandle instead.

BUG=

Review URL: https://codereview.chromium.org/666963002

git-svn-id: svn://svn.chromium.org/blink/trunk@184247 bbb929c8-8fbe-4397-9dbb-9b2b20218538