Bug 1725454 - Implement ui.caretBlinkCount on Windows. r=mhowell

This makes Firefox respect the following Windows registry key:

  Computer\HKEY_CURRENT_USER\Control Panel\Desktop\CaretTimeout

Which makes the caret stop blinking after a given timeout, and thus stop
wasting CPU.

Differential Revision: https://phabricator.services.mozilla.com/D122501

widget/windows/nsLookAndFeel.cpp

@@ -4,6 +4,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsLookAndFeel.h"
+#include <stdint.h>
 #include <windows.h>
 #include <shellapi.h>
 #include "nsStyleConsts.h"
@@ -369,6 +370,18 @@ nsresult nsLookAndFeel::NativeGetInt(IntID aID, int32_t& aResult) {
     case IntID::CaretBlinkTime:
       aResult = static_cast<int32_t>(::GetCaretBlinkTime());
       break;
+    case IntID::CaretBlinkCount: {
+      int32_t timeout = GetSystemParam(SPI_GETCARETTIMEOUT, 5000);
+      auto blinkTime = ::GetCaretBlinkTime();
+      if (timeout <= 0 || blinkTime <= 0) {
+        aResult = -1;
+        break;
+      }
+      // 2 * blinkTime because this integer is a full blink cycle.
+      aResult = std::ceil(float(timeout) / (2.0f * float(blinkTime)));
+      break;
+    }
+
     case IntID::CaretWidth:
       aResult = 1;
       break;

widget/windows/nsUXThemeConstants.h

@@ -177,6 +177,9 @@
 #ifndef SPI_GETMENUSHOWDELAY
 #  define SPI_GETMENUSHOWDELAY 106
 #endif  // SPI_GETMENUSHOWDELAY
+#ifndef SPI_GETCARETTIMEOUT
+#  define SPI_GETCARETTIMEOUT 0x2022
+#endif  // SPI_GETCARETTIMEOUT
 #ifndef WS_EX_LAYOUTRTL
 #  define WS_EX_LAYOUTRTL 0x00400000L  // Right to left mirroring
 #endif