mac: disable windowserver shadows on bots

This is essentially a debugging hack - we know that windowserver
crashes on the bots are caused by CoreGraphics trying to software-
composite shadows from a window layer, and we know that these crashes
only happen on VMWare bots.

Bug: 899286
Change-Id: I531e6008ca30978dfb0f97562387af58cb53dd92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1976016Reviewed-by: ccameron <ccameron@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728531}

chrome/browser/ui/cocoa/apps/native_app_window_cocoa_browsertest.mm

@@ -482,7 +482,9 @@ IN_PROC_BROWSER_TEST_F(NativeAppWindowCocoaBrowserTest, Frameless) {
 
   // Windows created with NSBorderlessWindowMask by default don't have shadow,
   // but packaged apps should always have one.
-  EXPECT_TRUE([ns_window hasShadow]);
+  // This specific check is disabled because shadows are disabled on the
+  // bots - see https://crbug.com/899286.
+  // EXPECT_TRUE([ns_window hasShadow]);
 
   // Since the window has no constraints, it should have all of the following
   // style mask bits.

components/remote_cocoa/app_shim/native_widget_ns_window_bridge.mm

@@ -49,6 +49,25 @@ using remote_cocoa::mojom::WindowVisibilityState;
 
 namespace {
 constexpr auto kUIPaintTimeout = base::TimeDelta::FromSeconds(5);
+
+bool AreWindowShadowsDisabled() {
+  // When:
+  // 1) Shadows are being generated by the window server
+  // 2) The window with the shadow has a layer (all of Chrome's do)
+  // 3) Software compositing is in use (it is in most test configs, which
+  //    run in VMs)
+  // 4) There are many windows in use at once (they are when running
+  //    test in parallel)
+  // The window server seems to crash with distressing frequency. To hopefully
+  // mitigate that, disable window shadows when running on a bot.
+  // For context on this see:
+  //   https://crbug.com/899286
+  //   https://crbug.com/828031
+  //   https://crbug.com/515627, especially #63 and #67
+  static bool is_headless = getenv("CHROME_HEADLESS") != nullptr;
+  return is_headless;
+}
+
 }  // namespace
 
 // The NSView that hosts the composited CALayer drawing the UI. It fills the
@@ -440,7 +459,8 @@ void NativeWidgetNSWindowBridge::InitWindow(
                               NSWindowCollectionBehaviorParticipatesInCycle];
   }
 
-  [window_ setHasShadow:params->has_window_server_shadow];
+  [window_ setHasShadow:params->has_window_server_shadow &&
+                        !AreWindowShadowsDisabled()];
   // Don't allow dragging sheets.
   if (params->modal_type == ui::MODAL_TYPE_WINDOW)
     [window_ setMovable:NO];

ui/views/cocoa/bridged_native_widget_unittest.mm

@@ -899,7 +899,9 @@ TEST_F(BridgedNativeWidgetInitTest, InitNotCalled) {
 }
 
 // Tests the shadow type given in InitParams.
-TEST_F(BridgedNativeWidgetInitTest, ShadowType) {
+// Disabled because shadows are disabled on the bots - see
+// https://crbug.com/899286.
+TEST_F(BridgedNativeWidgetInitTest, DISABLED_ShadowType) {
   // Verify Widget::InitParam defaults and arguments added from SetUp().
   EXPECT_EQ(Widget::InitParams::TYPE_WINDOW_FRAMELESS, type_);
   EXPECT_EQ(Widget::InitParams::WindowOpacity::kOpaque, opacity_);