Reland "Turn tab hover cards on by default on TOT."

This reverts commit 6379817e.

Reason for revert: Heap use after free that caused original revert has been fixed (see crbug/998642).

Original change's description:
> Revert "Turn tab hover cards on by default on TOT."
> 
> This reverts commit 6381a942.
> 
> Reason for revert: Causing heap use after free on ASAN bots.
> https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=unit_tests&tests=TabStripTest.TabCloseButtonVisibilityWhenNotStacked
> https://ci.chromium.org/p/chromium/builders/ci/Mac%20ASan%2064%20Tests%20%281%29/55741
> https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8905195500078197360/+/steps/unit_tests/0/logs/Deterministic_failure:_TabStripTest.TabCloseButtonVisibilityWhenNotStacked__x2f_0__status_CRASH_/0
> 
> Original change's description:
> > Turn tab hover cards on by default on TOT.
> > 
> > Stable approval has been given for 76 in crbug/962604.
> > 
> > Bug: 910739
> > Change-Id: If66c3c8954794126ff194c3d681c3cc71ec20759
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1747977
> > Commit-Queue: Caroline Rising <corising@chromium.org>
> > Reviewed-by: Peter Boström <pbos@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#686596}
> 
> TBR=pbos@chromium.org,corising@chromium.org
> 
> Change-Id: I361c919fb44bbe44aa7e028845693b44429f51d6
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 910739
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1753844
> Reviewed-by: Alan Cutter <alancutter@chromium.org>
> Commit-Queue: Alan Cutter <alancutter@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#686743}

TBR=alancutter@chromium.org,pbos@chromium.org,corising@chromium.org

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

Bug: 910739
Change-Id: I7888f967ddfd2d7a3e3aa15256e3b4ba808967cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1778983Reviewed-by: Caroline Rising <corising@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Commit-Queue: Caroline Rising <corising@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692114}

chrome/browser/ui/ui_features.cc

@@ -50,7 +50,7 @@ const base::Feature kTabGroups{"TabGroups", base::FEATURE_DISABLED_BY_DEFAULT};
 // Enables popup cards containing tab information when hovering over a tab.
 // https://crbug.com/910739
 const base::Feature kTabHoverCards{"TabHoverCards",
-                                   base::FEATURE_DISABLED_BY_DEFAULT};
+                                   base::FEATURE_ENABLED_BY_DEFAULT};
 // Parameter name used for tab hover cards user study.
 // TODO(corising): Removed this after tab hover cards user study.
 const char kTabHoverCardsFeatureParameterName[] = "setting";

chrome/browser/ui/views/tabs/tab_unittest.cc

@@ -16,6 +16,7 @@
 #include "chrome/browser/ui/tabs/tab_group_visual_data.h"
 #include "chrome/browser/ui/tabs/tab_types.h"
 #include "chrome/browser/ui/tabs/tab_utils.h"
+#include "chrome/browser/ui/ui_features.h"
 #include "chrome/browser/ui/views/tabs/alert_indicator.h"
 #include "chrome/browser/ui/views/tabs/fake_base_tab_strip_controller.h"
 #include "chrome/browser/ui/views/tabs/tab_close_button.h"
@@ -486,6 +487,10 @@ TEST_F(TabTest, LayoutAndVisibilityOfElements) {
 // Regression test for http://crbug.com/420313: Confirms that any child Views of
 // Tab do not attempt to provide their own tooltip behavior/text.
 TEST_F(TabTest, TooltipProvidedByTab) {
+  // This test isn't relevant when tab hover cards are enabled since tab
+  // tooltips are then disabled.
+  if (base::FeatureList::IsEnabled(features::kTabHoverCards))
+    return;
   Widget widget;
   InitWidget(&widget);
 
@@ -500,9 +505,9 @@ TEST_F(TabTest, TooltipProvidedByTab) {
   data.favicon = gfx::ImageSkia::CreateFrom1xBitmap(bitmap);
 
   data.title = base::UTF8ToUTF16(
-      "This is a really long tab title that would case views::Label to provide "
-      "its own tooltip; but Tab should disable that feature so it can provide "
-      "the tooltip instead.");
+      "This is a really long tab title that would cause views::Label to "
+      "provide its own tooltip; but Tab should disable that feature so it can "
+      "provide the tooltip instead.");
 
   // Test both with and without an indicator showing since the tab tooltip text
   // should include a description of the alert state when the indicator is