Bug 1394710 - Set process priority class on Windows r=aklotz

Fairly straightforward. Using an idle priority class for
background, which mirrors what I am observing of Chromium in
Process Explorer.

MozReview-Commit-ID: 2mimYN7aJOy

--HG--
extra : rebase_source : 18d992209178fc1f08d281920976881159af8f19

hal/moz.build

@@ -38,6 +38,7 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'android':
     ]
     UNIFIED_SOURCES += [
         'android/AndroidSensor.cpp',
+        'fallback/FallbackProcessPriority.cpp',
     ]
     # AndroidHal.cpp cannot be built in unified mode because it relies on HalImpl.h.
     SOURCES += [
@@ -48,6 +49,7 @@ elif CONFIG['OS_TARGET'] == 'Linux':
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackSensor.cpp',
         'fallback/FallbackVibration.cpp',
+        'fallback/FallbackProcessPriority.cpp',
     ]
     if CONFIG['MOZ_ENABLE_DBUS']:
         UNIFIED_SOURCES += [
@@ -61,6 +63,7 @@ elif CONFIG['OS_TARGET'] == 'WINNT':
     UNIFIED_SOURCES += [
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackVibration.cpp',
+        'windows/WindowsProcessPriority.cpp',
         'windows/WindowsSensor.cpp',
     ]
     # WindowsBattery.cpp cannot be built in unified mode because it relies on HalImpl.h.
@@ -72,12 +75,14 @@ elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'cocoa':
         'cocoa/CocoaBattery.cpp',
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackVibration.cpp',
+        'fallback/FallbackProcessPriority.cpp',
     ]
 elif CONFIG['OS_TARGET'] in ('OpenBSD', 'NetBSD', 'FreeBSD', 'DragonFly'):
     UNIFIED_SOURCES += [
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackSensor.cpp',
         'fallback/FallbackVibration.cpp',
+        'fallback/FallbackProcessPriority.cpp',
     ]
     if CONFIG['MOZ_ENABLE_DBUS']:
         UNIFIED_SOURCES += [
@@ -93,12 +98,12 @@ else:
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackSensor.cpp',
         'fallback/FallbackVibration.cpp',
+        'fallback/FallbackProcessPriority.cpp',
     ]
 
 # Fallbacks for backends no longer implemented.
 UNIFIED_SOURCES += [
     'fallback/FallbackDiskSpaceWatcher.cpp',
-    'fallback/FallbackProcessPriority.cpp',
 ]
 
 # Fallbacks for backends implemented on Android only.

hal/windows/WindowsProcessPriority.cpp

@@ -0,0 +1,43 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "Hal.h"
+#include "HalLog.h"
+
+#include <Windows.h>
+
+using namespace mozilla::hal;
+
+namespace mozilla {
+namespace hal_impl {
+
+bool
+SetProcessPrioritySupported()
+{
+  return true;
+}
+
+void
+SetProcessPriority(int aPid, ProcessPriority aPriority)
+{
+  HAL_LOG("WindowsProcessPriority - SetProcessPriority(%d, %s)\n",
+          aPid, ProcessPriorityToString(aPriority));
+
+  HANDLE hProcess = ::OpenProcess(PROCESS_SET_INFORMATION, false, aPid);
+  if (hProcess) {
+    DWORD priority = NORMAL_PRIORITY_CLASS;
+    if (aPriority == PROCESS_PRIORITY_BACKGROUND ||
+        aPriority == PROCESS_PRIORITY_BACKGROUND_PERCEIVABLE) {
+      priority = IDLE_PRIORITY_CLASS;
+    }
+    ::SetPriorityClass(hProcess, priority);
+    ::CloseHandle(hProcess);
+  }
+
+  HAL_LOG("WindowsProcessPriority - priority set to %d for pid %d\n",
+          aPriority, aPid);
+}
+
+} // namespace hal_impl
+} // namespace mozilla