Make message center always scroll up upon notification removal.

Add a switch to enable it. This feature would fix the problem when a large notification moves downwards, it is partially obstructed.

asvitkine: Please review histograms.xml

BUG=

Review URL: https://codereview.chromium.org/493303002

Cr-Commit-Position: refs/heads/master@{#292017}

8 files changed, 64 insertions, 1 deletions

diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 2ac3000..32cc37e 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -14697,6 +14697,14 @@ Do you accept?
     <message name="IDS_FLAGS_ENABLE_EXPERIMENTAL_HOTWORDING_DESCRIPTION" desc="Description of about:flags option for hotword detection.">
       Enables experimental 'Ok Google' hotword detection features, such as using the built-in extension. The hotword extension from the Chrome Web Store will no longer be used.
     </message>
+
+    <!-- Message center strings -->
+    <message name="IDS_FLAGS_ENABLE_MESSAGE_CENTER_ALWAYS_SCROLL_UP_UPON_REMOVAL_NAME" desc="Name of about:flags option for message center always scroll up experiment.">
+      Enable experiments that message center always scroll up upon notification removal.
+    </message>
+    <message name="IDS_FLAGS_ENABLE_MESSAGE_CENTER_ALWAYS_SCROLL_UP_UPON_REMOVAL_DESCRIPTION" desc="Description of about:flags option for message center always scroll up experiment.">
+      Enables experiment that message center always scroll up when a notification is removed.
+    </message>
   </messages>
   </release>
 </grit>
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index e03e238..ce9dfaf 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -46,6 +46,8 @@
 #include "chrome/common/chrome_version_info.h"
 #include "components/data_reduction_proxy/common/data_reduction_proxy_switches.h"
 #include "components/omnibox/omnibox_switches.h"
+#else
+#include "ui/message_center/message_center_switches.h"
 #endif
 
 #if defined(USE_ASH)
@@ -1907,6 +1909,16 @@ const Experiment kExperiments[] = {
     kOsAll,
     MULTI_VALUE_TYPE(kAutofillSyncCredentialChoices)
   },
+#if !defined(OS_ANDROID)
+  {
+    "enable-message-center-always-scroll-up-upon-notification-removal",
+    IDS_FLAGS_ENABLE_MESSAGE_CENTER_ALWAYS_SCROLL_UP_UPON_REMOVAL_NAME,
+    IDS_FLAGS_ENABLE_MESSAGE_CENTER_ALWAYS_SCROLL_UP_UPON_REMOVAL_DESCRIPTION,
+    kOsDesktop,
+    SINGLE_VALUE_TYPE(
+        switches::kEnableMessageCenterAlwaysScrollUpUponNotificationRemoval)
+  },
+#endif
   // NOTE: Adding new command-line switches requires adding corresponding
   // entries to enum "LoginCustomFlags" in histograms.xml. See note in
   // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 278c7ee..335ca07 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -43954,6 +43954,8 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="1821723343" label="disable-saml-signin"/>
   <int value="1844110073" label="enable-app-view"/>
   <int value="1855524566" label="allow-insecure-websocket-from-https-origin"/>
+  <int value="1861251313"
+      label="enable-message-center-always-scroll-up-upon-notification-removal"/>
   <int value="1900529524" label="disable-touch-drag-drop"/>
   <int value="1906942630" label="enable-easy-unlock"/>
   <int value="1930901873" label="disable-sync-app-list"/>
diff --git a/ui/message_center/BUILD.gn b/ui/message_center/BUILD.gn
index 03a6d10..bca5793 100644
--- a/ui/message_center/BUILD.gn
+++ b/ui/message_center/BUILD.gn
@@ -54,6 +54,8 @@ component("message_center") {
       "message_center_tray.h",
       "message_center_tray_delegate.h",
       "message_center_types.h",
+      "message_center_switches.h",
+      "message_center_switches.cc",
       "notification.cc",
       "notification.h",
       "notification_blocker.cc",
diff --git a/ui/message_center/message_center.gyp b/ui/message_center/message_center.gyp
index d163ee4..c1ece6a 100644
--- a/ui/message_center/message_center.gyp
+++ b/ui/message_center/message_center.gyp
@@ -57,6 +57,8 @@
         'message_center_observer.h',
         'message_center_style.cc',
         'message_center_style.h',
+        'message_center_switches.cc',
+        'message_center_switches.h',
         'message_center_tray.cc',
         'message_center_tray.h',
         'message_center_tray_delegate.h',
diff --git a/ui/message_center/message_center_switches.cc b/ui/message_center/message_center_switches.cc
new file mode 100644
index 0000000..4f82c1a
--- /dev/null
+++ b/ui/message_center/message_center_switches.cc
@@ -0,0 +1,15 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/message_center/message_center_switches.h"
+
+namespace switches {
+
+// Enables message center to always move other notifications upwards when a
+// notification is removed, no matter whether the message center is displayed
+// top down or not.
+const char kEnableMessageCenterAlwaysScrollUpUponNotificationRemoval[] =
+    "enable-message-center-always-scroll-up-upon-notification-removal";
+
+}  // namespace switches
diff --git a/ui/message_center/message_center_switches.h b/ui/message_center/message_center_switches.h
new file mode 100644
index 0000000..be4692e
--- /dev/null
+++ b/ui/message_center/message_center_switches.h
@@ -0,0 +1,18 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_MESSAGE_CENTER_MESSAGE_CENTER_SWITCHES_H_
+#define UI_MESSAGE_CENTER_MESSAGE_CENTER_SWITCHES_H_
+
+#include "base/compiler_specific.h"
+#include "ui/message_center/message_center_export.h"
+
+namespace switches {
+
+MESSAGE_CENTER_EXPORT extern const char
+    kEnableMessageCenterAlwaysScrollUpUponNotificationRemoval[];
+
+}  // namespace switches
+
+#endif  // UI_MESSAGE_CENTER_MESSAGE_CENTER_SWITCHES_H_
diff --git a/ui/message_center/views/message_center_view.cc b/ui/message_center/views/message_center_view.cc
index 2716b39..5b3ee28 100644
--- a/ui/message_center/views/message_center_view.cc
+++ b/ui/message_center/views/message_center_view.cc
@@ -7,6 +7,7 @@
 #include <list>
 #include <map>
 
+#include "base/command_line.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop.h"
 #include "base/stl_util.h"
@@ -19,6 +20,7 @@
 #include "ui/gfx/size.h"
 #include "ui/message_center/message_center.h"
 #include "ui/message_center/message_center_style.h"
+#include "ui/message_center/message_center_switches.h"
 #include "ui/message_center/message_center_tray.h"
 #include "ui/message_center/message_center_types.h"
 #include "ui/message_center/views/message_center_button_bar.h"
@@ -418,7 +420,9 @@ void MessageListView::DoUpdateIfPossible() {
     return;
   }
 
-  if (top_down_)
+  if (top_down_ ||
+      CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableMessageCenterAlwaysScrollUpUponNotificationRemoval))
     AnimateNotificationsBelowTarget();
   else
     AnimateNotificationsAboveTarget();