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];
+  // 10.10+
+  double on_period_ms = [defaults
+      doubleForKey:@"NSTextInsertionPointBlinkPeriodOn"];
+  double off_period_ms = [defaults
+      doubleForKey:@"NSTextInsertionPointBlinkPeriodOff"];
+  // 10.9
+  double period_ms = [defaults
+      doubleForKey:@"NSTextInsertionPointBlinkPeriod"];
+  if (on_period_ms == 0.0 && off_period_ms == 0.0 && period_ms == 0.0)
+    return false;
+  // Neither Blink nor Views support having separate on and off intervals, so
+  // this function takes the average. There's a special case: setting
+  // on_period_ms very high functions to permanently enable the cursor, which is
+  // what happens when the blink period in Blink/Views is set to 0. Setting
+  // off_period_ms very high would disable the cursor entirely, but Blink/Views
+  // do not support that so it's not implemented here.
+  if (on_period_ms > kMaximumReasonableIntervalMs ||
+      period_ms > kMaximumReasonableIntervalMs) {
+    *delta = base::TimeDelta();
+  } else if (on_period_ms || off_period_ms) {
+    *delta = base::TimeDelta::FromMillisecondsD(
+        (on_period_ms + off_period_ms) / 2);
+  } else {
+    *delta = base::TimeDelta::FromMilliseconds(period_ms);
+  }
+  return true;
+}
+
+}  // namespace ui