Bug 1620145: Part 2 - Add AndroidProcessPriority.cpp to hal; r=gsvelto,geckoview-reviewers,snorp

This patch is pretty straightforward: it translates Gecko priority levels
into GeckoView priority levels and then sends it up to GV's
`GeckoProcessManager` via JNI.

We do assume that the process is content, but if we try to do that on a
non-content process, it's just a no-op. We can expand this coverage to other
process types later as necessary.

Differential Revision: https://phabricator.services.mozilla.com/D68418

--HG--
extra : moz-landing-system : lando

hal/android/AndroidProcessPriority.cpp

@@ -0,0 +1,60 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+#include "Hal.h"
+
+#include "GeneratedJNIWrappers.h"
+
+/**
+ * Bucket the Gecko HAL process priority level into one of the three Android
+ * priority levels.
+ */
+static mozilla::java::ServiceAllocator::PriorityLevel::LocalRef
+ToJavaPriorityLevel(const ProcessPriority aPriority) {
+  if (aPriority >= PROCESS_PRIORITY_FOREGROUND) {
+    return mozilla::java::ServiceAllocator::PriorityLevel::FOREGROUND();
+  } else if (aPriority <= PROCESS_PRIORITY_PREALLOC &&
+             aPriority >= PROCESS_PRIORITY_BACKGROUND_PERCEIVABLE) {
+    return mozilla::java::ServiceAllocator::PriorityLevel::BACKGROUND();
+  }
+
+  return mozilla::java::ServiceAllocator::PriorityLevel::IDLE();
+}
+
+namespace mozilla {
+namespace hal_impl {
+
+bool SetProcessPrioritySupported() { return true; }
+
+void SetProcessPriority(int aPid, ProcessPriority aPriority) {
+  if (aPriority == PROCESS_PRIORITY_MASTER) {
+    // This is the parent process itself, which we do not control.
+    return;
+  }
+
+  const int32_t intPriority = static_cast<int32_t>(aPriority);
+  if (intPriority < 0 || intPriority >= NUM_PROCESS_PRIORITY) {
+    return;
+  }
+
+  auto contentProcType = java::GeckoProcessType::CONTENT();
+  auto selector =
+      java::GeckoProcessManager::Selector::New(contentProcType, aPid);
+  auto priorityLevel = ToJavaPriorityLevel(aPriority);
+
+  // To Android, a lower-valued integer is a higher relative priority.
+  // We take the integer value of the enum and subtract it from the value
+  // of the highest Gecko priority level to obtain a 0-based indicator of
+  // the relative priority within the Java PriorityLevel.
+  const int32_t relativeImportance =
+      (static_cast<int32_t>(NUM_PROCESS_PRIORITY) - 1) - intPriority;
+
+  java::GeckoProcessManager::SetProcessPriority(selector, priorityLevel,
+                                                relativeImportance);
+}
+
+}  // namespace hal_impl
+}  // namespace mozilla

hal/moz.build

@@ -40,8 +40,8 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'android':
         '/widget/android',
     ]
     UNIFIED_SOURCES += [
+        'android/AndroidProcessPriority.cpp',
         'android/AndroidSensor.cpp',
-        'fallback/FallbackProcessPriority.cpp',
     ]
     # AndroidHal.cpp cannot be built in unified mode because it relies on HalImpl.h.
     SOURCES += [