Mac: Deflake AppListServiceInteractiveTest.SwitchAppListProfilesDuringSearch

This is flaky because the app list ends up trying to read an ImageSkia
on one of Cocoa's background threads.

While NSView has a `canDrawConcurrently` function, AppKit is not calling
it in the case that is making this test flaky. The documentation says,
"The default is NO for most types of views.." [sic], and I've verified
it is `NO` and tried overriding it, but it was just never called.

However, having -[NSView canDraw] return `NO` seems to work fine.
Returning NO when there is no message loop ensures a draw only occurs on
a thread that Chrome created (not one of Cocoa's background threads),
and doesn't raise any DEPS issues.

BUG=417148, 415264

Review URL: https://codereview.chromium.org/599803002

Cr-Commit-Position: refs/heads/master@{#296591}

chrome/browser/ui/app_list/app_list_service_interactive_uitest.cc

@@ -49,25 +49,18 @@ class AppListServiceInteractiveTest : public InProcessBrowserTest {
 #if defined(OS_CHROMEOS)
 #define MAYBE_ShowAndDismiss DISABLED_ShowAndDismiss
 #define MAYBE_SwitchAppListProfiles DISABLED_SwitchAppListProfiles
+#define MAYBE_SwitchAppListProfilesDuringSearch \
+    DISABLED_SwitchAppListProfilesDuringSearch
 #define MAYBE_ShowAppListNonDefaultProfile \
     DISABLED_ShowAppListNonDefaultProfile
 #define MAYBE_DeleteShowingAppList DISABLED_DeleteShowingAppList
 #else
 #define MAYBE_ShowAndDismiss ShowAndDismiss
 #define MAYBE_SwitchAppListProfiles SwitchAppListProfiles
-#define MAYBE_ShowAppListNonDefaultProfile ShowAppListNonDefaultProfile
-#define MAYBE_DeleteShowingAppList DeleteShowingAppList
-#endif
-
-// SwitchAppListProfilesDuringSearch disabled on ChromeOS for reasons above.
-// Disabled on Mac due to an AppKit bug which makes it flaky in rare cases.
-// http://crbug.com/417148.
-#if defined(OS_CHROMEOS) || defined(OS_MACOSX)
-#define MAYBE_SwitchAppListProfilesDuringSearch \
-    DISABLED_SwitchAppListProfilesDuringSearch
-#else
 #define MAYBE_SwitchAppListProfilesDuringSearch \
     SwitchAppListProfilesDuringSearch
+#define MAYBE_ShowAppListNonDefaultProfile ShowAppListNonDefaultProfile
+#define MAYBE_DeleteShowingAppList DeleteShowingAppList
 #endif
 
 // Show the app list, then dismiss it.

ui/app_list/cocoa/apps_search_results_controller.mm

@@ -6,6 +6,7 @@
 
 #include "base/mac/foundation_util.h"
 #include "base/mac/mac_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/sys_string_conversions.h"
 #include "skia/ext/skia_utils_mac.h"
 #include "ui/app_list/app_list_constants.h"
@@ -401,6 +402,15 @@ const NSBackgroundStyle kBackgroundHovered = NSBackgroundStyleRaised;
       [self delegate]);
 }
 
+- (BOOL)canDraw {
+  // AppKit doesn't call -[NSView canDrawConcurrently] which would have told it
+  // that this is unsafe. Returning true from canDraw only if there is a message
+  // loop ensures that no drawing occurs on a background thread. Without this,
+  // ImageSkia can assert when trying to get bitmaps. http://crbug.com/417148.
+  // This means unit tests will always return 'NO', but that's OK.
+  return !!base::MessageLoop::current() && [super canDraw];
+}
+
 - (void)mouseDown:(NSEvent*)theEvent {
   [[self controller] mouseDown:theEvent];
   [super mouseDown:theEvent];