Rename IsSplitViewModeActive() to InSplitViewMode().

To be consistent with InTabletMode/ClamshellModeSplitView() functions,
rename IsSplitViewModeActive() function to InSplitViewMode().
Also delete Shell::IsSplitViewModeActive() function as it just calls
into the same function that SplitViewController provides.

No functionality is changed in this CL.

Bug: 890029
Change-Id: Ife37ee19d5af737ae8c1fc66ff42e8ef26fdc200
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1579244
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Mitsuru Oshima (Slow 4/22-26) <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654205}
31 files changed