Update CSS prefers-reduced-motion dynamically on Mac and Windows

Previously the content-side support for reduced motion for a frame was
static and would not react to changes in the system settings until you
created a new frame. This CL listens for notifications and recomputes
the webkit preferences when that happens (which then causes the new
prefers-reduced-motion value to be calculated).

This CL also introduces a caching mechanism for the system setting, to
avoid potentially expensive recomputation.

Test: Tested manually on MacOS and Windows devices.
Bug: 722548
Change-Id: I6be0822cc40a697a4373fbf53888d2219e5890f2
Reviewed-on: https://chromium-review.googlesource.com/c/1418498
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628406}

content/browser/accessibility/browser_accessibility_state_impl.h

@@ -10,10 +10,16 @@
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
+#include "build/build_config.h"
 #include "content/public/browser/browser_accessibility_state.h"
 #include "ui/accessibility/ax_mode.h"
 #include "ui/accessibility/ax_mode_observer.h"
 
+#if defined(OS_WIN)
+#include <memory>
+#include "ui/gfx/win/singleton_hwnd_observer.h"
+#endif
+
 namespace content {
 
 // The BrowserAccessibilityState class is used to determine if Chrome should be
@@ -93,6 +99,11 @@ class CONTENT_EXPORT BrowserAccessibilityStateImpl
 
   bool disable_hot_tracking_;
 
+#if defined(OS_WIN)
+  // Only used on Windows
+  std::unique_ptr<gfx::SingletonHwndObserver> singleton_hwnd_observer_;
+#endif
+
   DISALLOW_COPY_AND_ASSIGN(BrowserAccessibilityStateImpl);
 };
 

content/browser/accessibility/browser_accessibility_state_impl_mac.mm

@@ -7,6 +7,8 @@
 #import <Cocoa/Cocoa.h>
 
 #include "base/metrics/histogram_macros.h"
+#include "content/browser/web_contents/web_contents_impl.h"
+#include "ui/gfx/animation/animation.h"
 
 @interface NSWorkspace (Partials)
 
@@ -23,7 +25,39 @@
 
 namespace content {
 
-void BrowserAccessibilityStateImpl::PlatformInitialize() {}
+namespace {
+void SetupAccessibilityDisplayOptionsNotifier() {
+  // We need to call into gfx::Animation and WebContentsImpl on the UI thread,
+  // so ensure that we setup the notification on the correct thread.
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  if (@available(macOS 10.10, *)) {
+    // Listen to accessibility display options changing, so that we can update
+    // the renderer for the prefers reduced motion settings.
+    //
+    // BrowserAccessibilityStateImpl is a deliberately leaked singleton, so we
+    // don't need to record the notification token for later cleanup.
+    [[[NSWorkspace sharedWorkspace] notificationCenter]
+        addObserverForName:
+            NSWorkspaceAccessibilityDisplayOptionsDidChangeNotification
+                    object:nil
+                     queue:nil
+                usingBlock:^(NSNotification* notification) {
+                  gfx::Animation::UpdatePrefersReducedMotion();
+                  for (WebContentsImpl* wc :
+                       WebContentsImpl::GetAllWebContents()) {
+                    wc->GetRenderViewHost()->OnWebkitPreferencesChanged();
+                  }
+                }];
+  }
+}
+}  // namespace
+
+void BrowserAccessibilityStateImpl::PlatformInitialize() {
+  base::PostTaskWithTraits(
+      FROM_HERE, {BrowserThread::UI},
+      base::BindOnce(&SetupAccessibilityDisplayOptionsNotifier));
+}
 
 void BrowserAccessibilityStateImpl::UpdatePlatformSpecificHistograms() {
   // NOTE: This function is running on the file thread.

content/browser/accessibility/browser_accessibility_state_impl_win.cc

@@ -15,7 +15,9 @@
 #include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/strings/string_util.h"
+#include "content/browser/web_contents/web_contents_impl.h"
 #include "ui/accessibility/platform/ax_platform_node_win.h"
+#include "ui/gfx/animation/animation.h"
 
 namespace content {
 
@@ -67,11 +69,24 @@ class WindowsAccessibilityEnabler : public ui::IAccessible2UsageObserver {
   bool acc_name_called_ = false;
 };
 
+void OnWndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (message == WM_SETTINGCHANGE && wparam == SPI_SETCLIENTAREAANIMATION) {
+    gfx::Animation::UpdatePrefersReducedMotion();
+    for (WebContentsImpl* wc : WebContentsImpl::GetAllWebContents()) {
+      wc->GetRenderViewHost()->OnWebkitPreferencesChanged();
+    }
+  }
+}
+
 }  // namespace
 
 void BrowserAccessibilityStateImpl::PlatformInitialize() {
   ui::GetIAccessible2UsageObserverList().AddObserver(
       new WindowsAccessibilityEnabler());
+
+  singleton_hwnd_observer_.reset(
+      new gfx::SingletonHwndObserver(base::BindRepeating(&OnWndProc)));
 }
 
 void BrowserAccessibilityStateImpl::UpdatePlatformSpecificHistograms() {

ui/gfx/animation/animation.cc

@@ -4,6 +4,7 @@
 
 #include "ui/gfx/animation/animation.h"
 
+#include "base/message_loop/message_loop.h"
 #include "build/build_config.h"
 #include "ui/gfx/animation/animation_container.h"
 #include "ui/gfx/animation/animation_delegate.h"
@@ -16,6 +17,9 @@ namespace gfx {
 Animation::RichAnimationRenderMode Animation::rich_animation_rendering_mode_ =
     RichAnimationRenderMode::PLATFORM;
 
+// static
+base::Optional<bool> Animation::prefers_reduced_motion_;
+
 Animation::Animation(base::TimeDelta timer_interval)
     : timer_interval_(timer_interval),
       is_animating_(false),
@@ -107,20 +111,31 @@ bool Animation::ShouldRenderRichAnimationImpl() {
 }
 #endif
 
-#if !defined(OS_WIN) && !defined(OS_MACOSX)
+#if !defined(OS_WIN) && (!defined(OS_MACOSX) || defined(OS_IOS))
 // static
 bool Animation::ScrollAnimationsEnabledBySystem() {
   // Defined in platform specific files for Windows and OSX.
   return true;
 }
 
-bool Animation::PrefersReducedMotion() {
+// static
+void Animation::UpdatePrefersReducedMotion() {
+  // prefers_reduced_motion_ should only be modified on the UI thread.
+  // TODO(crbug.com/927163): DCHECK this assertion once tests are well-behaved.
+
   // By default, we assume that animations are enabled, to avoid impacting the
   // experience for users on systems that don't have APIs for reduced motion.
-  return false;
+  prefers_reduced_motion_ = false;
 }
 #endif
 
+// static
+bool Animation::PrefersReducedMotion() {
+  if (!prefers_reduced_motion_)
+    UpdatePrefersReducedMotion();
+  return *prefers_reduced_motion_;
+}
+
 bool Animation::ShouldSendCanceledFromStop() {
   return false;
 }

ui/gfx/animation/animation.h

@@ -8,6 +8,7 @@
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/optional.h"
 #include "base/time/time.h"
 #include "ui/gfx/animation/animation_container_element.h"
 #include "ui/gfx/animation/animation_export.h"
@@ -80,8 +81,9 @@ class ANIMATION_EXPORT Animation : public AnimationContainerElement {
   static bool ScrollAnimationsEnabledBySystem();
 
   // Determines whether the user desires reduced motion based on platform APIs.
-  // Should only be called from the browser process.
+  // Should only be called from the browser process, on the UI thread.
   static bool PrefersReducedMotion();
+  static void UpdatePrefersReducedMotion();
 
  protected:
   // Invoked from Start to allow subclasses to prepare for the animation.
@@ -128,6 +130,10 @@ class ANIMATION_EXPORT Animation : public AnimationContainerElement {
   // Time we started at.
   base::TimeTicks start_time_;
 
+  // Obtaining the PrefersReducedMotion system setting can be expensive, so it
+  // is cached in this boolean.
+  static base::Optional<bool> prefers_reduced_motion_;
+
   DISALLOW_COPY_AND_ASSIGN(Animation);
 };
 

ui/gfx/animation/animation_mac.mm

@@ -33,21 +33,18 @@ bool Animation::ScrollAnimationsEnabledBySystem() {
 }
 
 // static
-bool Animation::PrefersReducedMotion() {
-  // Because of sandboxing, OS settings should only be queried from the browser
-  // process.
-  DCHECK(base::MessageLoopCurrentForUI::IsSet() ||
-         base::MessageLoopCurrentForIO::IsSet());
+void Animation::UpdatePrefersReducedMotion() {
+  // prefers_reduced_motion_ should only be modified on the UI thread.
+  // TODO(crbug.com/927163): DCHECK this assertion once tests are well-behaved.
 
   // We default to assuming that animations are enabled, to avoid impacting the
   // experience for users on pre-10.12 systems.
-  bool prefers_reduced_motion = false;
+  prefers_reduced_motion_ = false;
   SEL sel = @selector(accessibilityDisplayShouldReduceMotion);
   if ([[NSWorkspace sharedWorkspace] respondsToSelector:sel]) {
-    prefers_reduced_motion =
+    prefers_reduced_motion_ =
         [[NSWorkspace sharedWorkspace] accessibilityDisplayShouldReduceMotion];
   }
-  return prefers_reduced_motion;
 }
 
 } // namespace gfx

ui/gfx/animation/animation_win.cc

@@ -6,6 +6,8 @@
 
 #include <windows.h>
 
+#include "base/message_loop/message_loop.h"
+
 namespace gfx {
 
 // static
@@ -24,12 +26,15 @@ bool Animation::ScrollAnimationsEnabledBySystem() {
 }
 
 // static
-bool Animation::PrefersReducedMotion() {
+void Animation::UpdatePrefersReducedMotion() {
+  // prefers_reduced_motion_ should only be modified on the UI thread.
+  // TODO(crbug.com/927163): DCHECK this assertion once tests are well-behaved.
+
   // We default to assuming that animations are enabled, to avoid impacting the
   // experience for users on systems that don't have SPI_GETCLIENTAREAANIMATION.
   BOOL win_anim_enabled = true;
   SystemParametersInfo(SPI_GETCLIENTAREAANIMATION, 0, &win_anim_enabled, 0);
-  return !win_anim_enabled;
+  prefers_reduced_motion_ = !win_anim_enabled;
 }
 
 } // namespace gfx