Improve pass through mode in ChromeVox

In particular, this change makes it so we precisely pass through only the next sequence of key downs/ups that follow the pass through shortcut (Search+Shift+Esc).
Previously, we would only partially pass through the shortcut after the Search+Shift+Esc command.

Test: browser_tests --gtest_filter=ChromeVox*.*
Change-Id: Ic9d41d35bd5cce47eb3151bdba6b435f385d56e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2104449Reviewed-by: Sara Kato <sarakato@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750813}

chrome/browser/resources/chromeos/accessibility/chromevox/background/keyboard_handler.js

@@ -15,14 +15,35 @@ goog.require('Output');
 goog.require('ChromeVoxKbHandler');
 goog.require('ChromeVoxPrefs');
 
+/**
+ * @enum {string}
+ * Internal pass through mode state (see usage below).
+ * @private
+ */
+const KeyboardPassThroughState_ = {
+  // No pass through is in progress.
+  NO_PASS_THROUGH: 'no_pass_through',
+
+  // The pass through shortcut command has been pressed (keydowns), waiting for
+  // user to release (keyups) all the shortcut keys.
+  PENDING_PASS_THROUGH_SHORTCUT_KEYUPS: 'pending_pass_through_keyups',
+
+  // The pass through shortcut command has been pressed and released, waiting
+  // for the user to press/release a shortcut to be passed through.
+  PENDING_SHORTCUT_KEYUPS: 'pending_shortcut_keyups'
+};
+
 BackgroundKeyboardHandler = class {
   constructor() {
-    /** @type {number} @private */
-    this.passThroughKeyUpCount_ = 0;
+    /** @private {!KeyboardPassThroughState_} */
+    this.passThroughState_ = KeyboardPassThroughState_.NO_PASS_THROUGH;
 
     /** @type {Set} @private */
     this.eatenKeyDowns_ = new Set();
 
+    /** @private {Set} */
+    this.passedThroughKeyDowns_ = new Set();
+
     document.addEventListener('keydown', this.onKeyDown.bind(this), false);
     document.addEventListener('keyup', this.onKeyUp.bind(this), false);
 
@@ -40,7 +61,17 @@ BackgroundKeyboardHandler = class {
   onKeyDown(evt) {
     EventSourceState.set(EventSourceType.STANDARD_KEYBOARD);
     evt.stickyMode = ChromeVox.isStickyModeOn();
+
+    // If somehow the user gets into a state where there are dangling key downs
+    // don't get a key up, clear the eaten key downs. This is detected by a set
+    // list of modifier flags.
+    if (!evt.altKey && !evt.ctrlKey && !evt.metaKey && !evt.shiftKey) {
+      this.eatenKeyDowns_.clear();
+      this.passedThroughKeyDowns_.clear();
+    }
+
     if (ChromeVox.passThroughMode) {
+      this.passedThroughKeyDowns_.add(evt.keyCode);
       return false;
     }
 
@@ -56,6 +87,10 @@ BackgroundKeyboardHandler = class {
         // ChromeVox has no range.
         (ChromeVoxState.instance.currentRange &&
          (evt.metaKey || evt.keyCode == 91))) {
+      if (ChromeVox.passThroughMode) {
+        this.passThroughState_ =
+            KeyboardPassThroughState_.PENDING_PASS_THROUGH_SHORTCUT_KEYUPS;
+      }
       evt.preventDefault();
       evt.stopPropagation();
       this.eatenKeyDowns_.add(evt.keyCode);
@@ -70,23 +105,32 @@ BackgroundKeyboardHandler = class {
    *     SpokenFeedbackEventRewriterDelegate::HandleKeyboardEvent.
    */
   onKeyUp(evt) {
-    // Reset pass through mode once a keyup (not involving the pass through
-    // key) is seen. The pass through command involves three keys.
-    if (ChromeVox.passThroughMode) {
-      if (this.passThroughKeyUpCount_ >= 3) {
-        ChromeVox.passThroughMode = false;
-        this.passThroughKeyUpCount_ = 0;
-      } else {
-        this.passThroughKeyUpCount_++;
-      }
-    }
-
     if (this.eatenKeyDowns_.has(evt.keyCode)) {
       evt.preventDefault();
       evt.stopPropagation();
       this.eatenKeyDowns_.delete(evt.keyCode);
     }
 
+    if (ChromeVox.passThroughMode) {
+      this.passedThroughKeyDowns_.delete(evt.keyCode);
+      if (this.passThroughState_ ==
+              KeyboardPassThroughState_.PENDING_PASS_THROUGH_SHORTCUT_KEYUPS &&
+          this.eatenKeyDowns_.size == 0) {
+        // All keys of the pass through shortcut command have been released.
+        // Ready to pass through the next shortcut.
+        this.passThroughState_ =
+            KeyboardPassThroughState_.PENDING_SHORTCUT_KEYUPS;
+      } else if (
+          this.passThroughState_ ==
+              KeyboardPassThroughState_.PENDING_SHORTCUT_KEYUPS &&
+          this.passedThroughKeyDowns_.size == 0) {
+        // All keys of the passed through shortcut have been released. Ready to
+        // go back to normal processing (aka no pass through).
+        ChromeVox.passThroughMode = false;
+        this.passThroughState_ = KeyboardPassThroughState_.NO_PASS_THROUGH;
+      }
+    }
+
     return false;
   }