Reland "[iOS] Enable the new Clear Browsing Data UI flag"

This reverts commit 7044d791.

Reason for revert: Since this is launching to 100% in M77 the flag should be at least enabled by default in M78.

Original change's description:
> Revert "[iOS] Enable the new Clear Browsing Data UI flag"
> 
> This reverts commit 9223cbe0.
> 
> Reason for revert: Not getting leadership-full approval before branch point; will rollout with Finch.
> 
> Original change's description:
> > [iOS] Enable the new Clear Browsing Data UI flag
> > 
> > This change is to enable the new-clear-browsing-data-ui flag.
> > 
> > The new Clear Browsing Data dialog adds the time range selection functionality
> > and shows browsing data volume details for each data type.
> > Launch Bug: crbug/627147
> > Screenshots: https://drive.google.com/open?id=1q1zJzB1abRsY1zCD4rLewvMxCnMr8WGf
> > 
> > Bug: 627147
> > Change-Id: If2e16f4697a7aac2308a430c48880eb2f0c58c19
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1624906
> > Reviewed-by: Rohit Rao <rohitrao@chromium.org>
> > Commit-Queue: Rohit Rao <rohitrao@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#662278}
> 
> TBR=rohitrao@chromium.org
> 
> # Not skipping CQ checks because original CL landed > 1 day ago.
> 
> Bug: 627147
> Change-Id: I26afad9076841353b0210f4537d8842aab9631e6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1635617
> Reviewed-by: Huanzhong Huang <huanzhong@chromium.org>
> Commit-Queue: Huanzhong Huang <huanzhong@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#664723}

TBR=rohitrao@chromium.org,huanzhong@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 627147
Change-Id: Ib4f4a1bda447bc4f28541191c99fd5427f2b3844
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1797180Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Huanzhong Huang <huanzhong@chromium.org>
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696052}

ios/chrome/browser/browsing_data/browsing_data_features.cc

@@ -5,7 +5,7 @@
 #include "ios/chrome/browser/browsing_data/browsing_data_features.h"
 
 const base::Feature kNewClearBrowsingDataUI{"NewClearBrowsingDataUI",
-                                            base::FEATURE_DISABLED_BY_DEFAULT};
+                                            base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kWebClearBrowsingData{"WebClearBrowsingData",
                                           base::FEATURE_DISABLED_BY_DEFAULT};