mac: use NSUserDefaults values for caret blink rate if present

ui/base/cocoa/defaults_utils.mm

+// Copyright 2016 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 <AppKit/AppKit.h>
+
+#include "base/logging.h"
+#include "ui/base/cocoa/defaults_utils.h"
+
+namespace ui {
+
+bool TextInsertionCaretBlinkPeriod(base::TimeDelta* delta) {
+  const int kMaximumReasonableIntervalMs = 60 * 1000;
+  NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
+  double on_period_ms = [defaults
+      floatForKey:@"NSTextInsertionPointBlinkPeriodOn"];
+  double off_period_ms = [defaults
+      floatForKey:@"NSTextInsertionPointBlinkPeriodOff"];

[Nico, 2016/08/25 19:40:37]

apparently it's NSTextInsertionPointBlinkPeriod in older os x'en, do we want to
query that too?

[Elly Fong-Jones, 2016/08/25 19:57:33]

Done.

+  if (on_period_ms == 0.0 && off_period_ms == 0.0)
+    return false;
+  // Neither Blink nor Views support having separate on and off intervals, so
+  // this function takes the average.
+  if (on_period_ms > kMaximumReasonableIntervalMs) {

[Nico, 2016/08/25 19:40:37]

why check this for on_period_ms but not off_period_ms? I would've expected

  on_period_ms = min(on_period_ms, kMaximumReasonableIntervalMs);
  off_period_ms = min(off_period_ms, kMaximumReasonableIntervalMs);

  *delta = base::TimeDelta::FromMillisecondsD(
        (on_period_ms + off_period_ms) / 2);

[Elly Fong-Jones, 2016/08/25 19:57:33]

Added explanation

+    *delta = base::TimeDelta();
+  } else {
+    *delta = base::TimeDelta::FromMillisecondsD(
+        (on_period_ms + off_period_ms) / 2);
+  }
+  return true;
+}
+
+}  // namespace ui