One accessibility tree per frame.

content/browser/accessibility/browser_accessibility_android.cc

Index: content/browser/accessibility/browser_accessibility_android.cc
diff --git a/content/browser/accessibility/browser_accessibility_android.cc b/content/browser/accessibility/browser_accessibility_android.cc
index 3cc4c5ec28f788e80dab529c74837def527eeada..71d4d401e88eeb078898568ee898aca138754d0d 100644
--- a/content/browser/accessibility/browser_accessibility_android.cc
+++ b/content/browser/accessibility/browser_accessibility_android.cc
@@ -303,7 +303,10 @@ const char* BrowserAccessibilityAndroid::GetClassName() const {
       class_name = "android.app.Dialog";
       break;
     case ui::AX_ROLE_ROOT_WEB_AREA:

[David Tseng, 2016/03/04 16:50:20]

So, AX_ROLE_WEB_AREA is no longer used?

[dmazzoni, 2016/03/07 21:35:32]

Yes. I was planning to delete it in a follow-up change, but that would touch a
lot of files so I didn't want to do it here.

-      class_name = "android.webkit.WebView";
+      if (GetParent() == nullptr)
+        class_name = "android.webkit.WebView";
+      else
+        class_name = "android.view.View";
       break;
     case ui::AX_ROLE_MENU_ITEM:
     case ui::AX_ROLE_MENU_ITEM_CHECK_BOX:
@@ -935,13 +938,13 @@ bool BrowserAccessibilityAndroid::Scroll(int direction) const {
   // Figure out the bounding box of the visible portion of this scrollable
   // view so we know how much to scroll by.
   gfx::Rect bounds;
-  if (GetRole() == ui::AX_ROLE_ROOT_WEB_AREA) {
+  if (GetRole() == ui::AX_ROLE_ROOT_WEB_AREA && !GetParent()) {
     // If this is the root web area, use the bounds of the view to determine
     // how big one page is.
     if (!manager()->delegate())
       return false;
     bounds = manager()->delegate()->AccessibilityGetViewBounds();
-  } else if (GetRole() == ui::AX_ROLE_WEB_AREA) {
+  } else if (GetRole() == ui::AX_ROLE_ROOT_WEB_AREA) {

[David Tseng, 2016/03/04 16:50:20]

&& GetParent()

[dmazzoni, 2016/03/07 21:35:32]

Done.

     // If this is a web area inside of an iframe, try to use the bounds of
     // the containing element.
     BrowserAccessibility* parent = GetParent();