Set keys to traverse accessibility tree. Using focus ring to highlight selected node.

chrome/browser/chromeos/accessibility/switch_access_event_handler.cc

+// Copyright 2017 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.
+
+#include "chrome/browser/chromeos/accessibility/switch_access_event_handler.h"
+
+#include "ash/shell.h"
+#include "base/logging.h"
+#include "chrome/browser/chromeos/accessibility/accessibility_manager.h"
+#include "chrome/browser/profiles/profile_manager.h"
+#include "chrome/common/extensions/extension_constants.h"
+#include "content/public/browser/render_view_host.h"
+#include "content/public/browser/render_widget_host.h"
+#include "extensions/browser/extension_host.h"
+#include "extensions/browser/extension_registry.h"
+#include "extensions/browser/process_manager.h"
+#include "ui/events/event.h"
+
+namespace chromeos {
+
+SwitchAccessEventHandler::SwitchAccessEventHandler() {
+  if (ash::Shell::HasInstance())
+    ash::Shell::GetInstance()->AddPreTargetHandler(this);
+}
+
+SwitchAccessEventHandler::~SwitchAccessEventHandler() {
+  if (ash::Shell::HasInstance())
+    ash::Shell::GetInstance()->RemovePreTargetHandler(this);
+}
+
+void SwitchAccessEventHandler::OnKeyEvent(ui::KeyEvent* event) {
+  DCHECK(event);
+  if (event->key_code() == ui::VKEY_1) {
+    CancelEvent(event);
+    if (event->type() == ui::ET_KEY_PRESSED && state_ == INACTIVE) {
+      state_ = ONE_KEY_DOWN;

[dmazzoni, 2017/02/24 23:06:54]

The state machine made a lot of sense for select-to-speak because it needed to
detect
a combination of Search key plus mouse events, but do nothing otherwise.

I think you can do something simpler here - just "eat" (cancel) all events
involving
the set of keys you care about, and forward them all to the extension. No state
machine required.

At least, I can't think of a reason to have one. There's no reason that Ctrl+1
needs to
do anything different than 1.

[elichtenberg, 2017/02/28 00:28:42]

Done.

+      LOG(ERROR) << "One key was pressed!";
+    } else if (event->type() == ui::ET_KEY_RELEASED && state_ == ONE_KEY_DOWN) {
+      state_ = INACTIVE;
+      LOG(ERROR) << "One key was released!";
+      bool result = DispatchKeyEventToSwitchAccess(*event);
+      LOG(ERROR) << "Result of dispatching one key was: " << std::boolalpha
+                 << result;
+    }
+  } else if (event->key_code() == ui::VKEY_2) {
+    CancelEvent(event);
+    if (event->type() == ui::ET_KEY_PRESSED && state_ == INACTIVE) {
+      state_ = TWO_KEY_DOWN;
+      LOG(ERROR) << "Two key was pressed!";
+    } else if (event->type() == ui::ET_KEY_RELEASED && state_ == TWO_KEY_DOWN) {
+      state_ = INACTIVE;
+      LOG(ERROR) << "Two key was released!";
+      bool result = DispatchKeyEventToSwitchAccess(*event);
+      LOG(ERROR) << "Result of dispatching two key was: " << std::boolalpha
+                 << result;
+    }
+  } else if (event->key_code() == ui::VKEY_3) {
+    CancelEvent(event);
+    if (event->type() == ui::ET_KEY_PRESSED && state_ == INACTIVE) {
+      state_ = THREE_KEY_DOWN;
+      LOG(ERROR) << "Three key was pressed!";
+    } else if (event->type() == ui::ET_KEY_RELEASED &&
+               state_ == THREE_KEY_DOWN) {
+      state_ = INACTIVE;
+      LOG(ERROR) << "Three key was released!";
+      bool result = DispatchKeyEventToSwitchAccess(*event);
+      LOG(ERROR) << "Result of dispatching three key was: " << std::boolalpha
+                 << result;
+    }
+  } else if (event->key_code() == ui::VKEY_4) {
+    CancelEvent(event);
+    if (event->type() == ui::ET_KEY_PRESSED && state_ == INACTIVE) {
+      state_ = FOUR_KEY_DOWN;
+      LOG(ERROR) << "Four key was pressed!";
+    } else if (event->type() == ui::ET_KEY_RELEASED &&
+               state_ == FOUR_KEY_DOWN) {
+      state_ = INACTIVE;
+      LOG(ERROR) << "Four key was released!";
+      bool result = DispatchKeyEventToSwitchAccess(*event);
+      LOG(ERROR) << "Result of dispatching four key was: " << std::boolalpha
+                 << result;
+    }
+  } else if (event->key_code() == ui::VKEY_5) {
+    CancelEvent(event);
+    if (event->type() == ui::ET_KEY_PRESSED && state_ == INACTIVE) {
+      state_ = FIVE_KEY_DOWN;
+      LOG(ERROR) << "Five key was pressed!";
+    } else if (event->type() == ui::ET_KEY_RELEASED &&
+               state_ == FIVE_KEY_DOWN) {
+      state_ = INACTIVE;
+      LOG(ERROR) << "Five key was released!";
+      bool result = DispatchKeyEventToSwitchAccess(*event);
+      LOG(ERROR) << "Result of dispatching five key was: " << std::boolalpha
+                 << result;
+    }
+  }
+}
+
+void SwitchAccessEventHandler::CancelEvent(ui::Event* event) {
+  DCHECK(event);
+  if (event->cancelable()) {
+    event->SetHandled();
+    event->StopPropagation();
+  }
+}
+
+bool SwitchAccessEventHandler::DispatchKeyEventToSwitchAccess(

[dmazzoni, 2017/02/24 23:06:54]

Please refactor this into a common utility function like
DispatchKeyEventToExtension() and have it take an extension id
as a parameter.

You can put it in:

chrome/browser/chromeos/accessibility/accessibility_util.h
chrome/browser/chromeos/accessibility/accessibility_util.cc

Then use that from select-to_speak_event_handler.cc, too.

[elichtenberg, 2017/02/28 00:28:42]

Done. Did event_handler_common.h and event_handler_common.cc

+    const ui::KeyEvent& event) {
+  if (!AccessibilityManager::Get())
+    return false;
+
+  content::BrowserContext* context = ProfileManager::GetActiveUserProfile();
+  if (!context)
+    return false;
+
+  const extensions::Extension* extension =
+      extensions::ExtensionRegistry::Get(context)->enabled_extensions().GetByID(
+          extension_misc::kSwitchAccessExtensionId);
+  if (!extension)
+    return false;
+
+  extensions::ExtensionHost* host =
+      extensions::ProcessManager::Get(context)->GetBackgroundHostForExtension(
+          extension->id());
+  if (!host)
+    return false;
+
+  content::RenderViewHost* rvh = host->render_view_host();
+  if (!rvh)
+    return false;
+
+  const content::NativeWebKeyboardEvent web_event(event);
+  rvh->GetWidget()->ForwardKeyboardEvent(web_event);
+  return true;
+}
+
+}  // namespace chromeos