Keep track of accessibility focus across windows.

content/browser/accessibility/browser_accessibility_cocoa.mm

Index: content/browser/accessibility/browser_accessibility_cocoa.mm
diff --git a/content/browser/accessibility/browser_accessibility_cocoa.mm b/content/browser/accessibility/browser_accessibility_cocoa.mm
index 78c8c0150fba5eecb312d45de79d63575453ab8e..d84882d5bb2a0d89b15188eed21f921f393657ed 100644
--- a/content/browser/accessibility/browser_accessibility_cocoa.mm
+++ b/content/browser/accessibility/browser_accessibility_cocoa.mm
@@ -675,7 +675,7 @@ bool InitializeAccessibilityTreeSearch(
 - (NSNumber*)focused {
   BrowserAccessibilityManager* manager = browserAccessibility_->manager();
   NSNumber* ret = [NSNumber numberWithBool:
-      manager->GetFocus(NULL) == browserAccessibility_];
+      manager->GetFocus() == browserAccessibility_];
   return ret;
 }
 
@@ -1132,7 +1132,9 @@ bool InitializeAccessibilityTreeSearch(
 - (NSArray*)selectedChildren {
   NSMutableArray* ret = [[[NSMutableArray alloc] init] autorelease];
   BrowserAccessibilityManager* manager = browserAccessibility_->manager();
-  BrowserAccessibility* focusedChild = manager->GetFocus(browserAccessibility_);
+  BrowserAccessibility* focusedChild = manager->GetFocus();
+  if (!focusedChild->IsDescendantOf(browserAccessibility_))
+    focusedChild = nullptr;
 
   // If it's not multiselectable, try to skip iterating over the
   // children.
@@ -2032,7 +2034,7 @@ bool InitializeAccessibilityTreeSearch(
     NSNumber* focusedNumber = value;
     BOOL focused = [focusedNumber intValue];
     if (focused)
-      manager->SetFocus(browserAccessibility_, true);
+      manager->SetFocus(*browserAccessibility_);

[David Tseng, 2016/01/28 02:00:56]

Btw, how does someone clear focus and is browserAccessibility_ guaranteed to be
non-null?

[dmazzoni, 2016/01/30 00:02:41]

Yes, browserAccessibility_ is non-null because BrowserAccessibilityCocoa
outlives the object it wraps.

What should clear focus mean, now that we're thinking about focus more globally?
Is there a specific use-case?

   }
   if ([attribute isEqualToString:NSAccessibilitySelectedTextRangeAttribute]) {
     NSRange range = [(NSValue*)value rangeValue];