Implement accessibility enhancements (issue #1217)

- Add new CefBrowserHost::SetAccessibilityState method for toggling
  accessibility state when readers are detected by the client.
- Add new CefAccessibilityHandler interface for the delivery of
  accessibility notifications to windowless (OSR) clients.
- Fix delivery of CefFocusHandler callbacks to windowless clients.
- cefclient: Add example windowless accessibility implementation on Windows and macOS.
- cefclient: Automatically detect screen readers on Windows and macOS.

tests/cefclient/browser/osr_accessibility_node.cc

@@ -0,0 +1,102 @@
+// Copyright 2017 The Chromium Embedded Framework Authors. Portions copyright
+// 2013 The Chromium Authors. All rights reserved. Use of this source code is
+// governed by a BSD-style license that can be found in the LICENSE file.
+
+// Base class implementation for CEF Acccessibility node. This is subclassed and
+// used by both IAccessible/NSAccessibility protocol implementation.
+
+#include "tests/cefclient/browser/osr_accessibility_node.h"
+
+#include "tests/cefclient/browser/osr_accessibility_helper.h"
+
+namespace client {
+
+OsrAXNode::OsrAXNode(CefRefPtr<CefDictionaryValue> value,
+                     OsrAccessibilityHelper* helper)
+    : node_id_(-1), platform_accessibility_(NULL), parent_(NULL),
+    accessibility_helper_(helper) {
+  UpdateValue(value);
+}
+
+void OsrAXNode::UpdateValue(CefRefPtr<CefDictionaryValue> value) {
+  if (value && value->HasKey("id")) {
+    node_id_ = value->GetInt("id");
+
+    if (value->HasKey("role"))
+      role_ = value->GetString("role");
+
+    if (value->HasKey("child_ids")) {
+      CefRefPtr<CefListValue> childs = value->GetList("child_ids");
+      // Reset child Ids
+      child_ids_.clear();
+      for(size_t idx = 0; idx < childs->GetSize(); idx++)
+        child_ids_.push_back(childs->GetInt(idx));
+    }
+    // Update Location
+    if (value->HasKey("location")) {
+      CefRefPtr<CefDictionaryValue> loc = value->GetDictionary("location");
+      if (loc) {
+        location_ = CefRect(loc->GetDouble("x"), loc->GetDouble("y"),
+                            loc->GetDouble("width"), loc->GetDouble("height"));
+      }
+    }
+    // Update offsets
+    if (value->HasKey("offset_container_id")) {
+      offset_container_id_ = value->GetInt("offset_container_id");
+    }
+    // Update attributes
+    if (value->HasKey("attributes")) {
+      attributes_ = value->GetDictionary("attributes");
+
+      if (attributes_ && attributes_->HasKey("name"))
+        name_ = attributes_->GetString("name");
+      if (attributes_ && attributes_->HasKey("value"))
+          value_ = attributes_->GetString("value");
+      if (attributes_ && attributes_->HasKey("description"))
+          description_ = attributes_->GetString("description");
+    }
+  }
+}
+
+CefWindowHandle OsrAXNode::GetWindowHandle() const {
+  if (accessibility_helper_)
+    return accessibility_helper_->GetWindowHandle();
+  return NULL;
+}
+
+CefRefPtr<CefBrowser> OsrAXNode::GetBrowser() const {
+  if (accessibility_helper_)
+    return accessibility_helper_->GetBrowser();
+  return NULL;
+}
+
+void OsrAXNode::SetParent(OsrAXNode* parent) {
+  parent_ = parent;
+}
+
+CefRect OsrAXNode::AxLocation() const {
+  CefRect loc = location_;
+  OsrAXNode* offsetNode = accessibility_helper_->GetNode(offset_container_id_);
+  // Add offset from parent Lcoation
+  if (offsetNode) {
+    CefRect offset = offsetNode->AxLocation();
+    loc.x += offset.x;
+    loc.y += offset.y;
+  }
+  return loc;
+}
+
+OsrAXNode* OsrAXNode::ChildAtIndex(int index) const {
+  if (index < GetChildCount())
+    return accessibility_helper_->GetNode(child_ids_[index]);
+  else
+    return NULL;
+}
+
+// Create and return the platform specific OsrAXNode Object
+OsrAXNode* OsrAXNode::CreateNode(CefRefPtr<CefDictionaryValue> value,
+                                 OsrAccessibilityHelper* helper) {
+  return new OsrAXNode(value, helper);
+}
+
+}  // namespace client