Reland "Shelf should not update state when entering overview mode."

This is a reland of b14d52639cd18c4d99cb7d436ff2083e9c5f600e

Original change's description:
> Shelf should not update state when entering overview mode.
> 
> Bug: 1033219
> Change-Id: Iaf760307c32a67e3ef5da7308235a3c297c2d0af
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2242832
> Reviewed-by: Xiyuan Xia <[email protected]>
> Reviewed-by: Yulun Wu <[email protected]>
> Reviewed-by: Toni Baržić <[email protected]>
> Commit-Queue: Yulun Wu <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#782657}

Bug: 1033219
Change-Id: I329540b99f46e4532c5c4ea1e8d5876fb430251a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2270798
Reviewed-by: Xiyuan Xia <[email protected]>
Reviewed-by: Yulun Wu <[email protected]>
Commit-Queue: Yulun Wu <[email protected]>
Cr-Commit-Position: refs/heads/master@{#783260}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 01097ee..5b9b62aa 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -689,6 +689,11 @@
 const char kMacCoreLocationImplementationDescription[] =
     "Enables usage of the Core Location APIs on macOS for geolocation";
 
+const char kMaintainShelfStateWhenEnteringOverviewName[] =
+    "Allow Home Launcher Shelf In Overview";
+const char kMaintainShelfStateWhenEnteringOverviewDescription[] =
+    "Maintains shelf state when entering and exiting overview mode.";
+
 const char kWinrtGeolocationImplementationName[] =
     "WinRT Geolocation Implementation";
 const char kWinrtGeolocationImplementationDescription[] =