Bug 1200343 - Implment PrefsHelper native calls; r=snorp

This patch implements the PrefsHelper native calls for getting prefs;

widget/android/PrefsHelper.h

@@ -0,0 +1,78 @@
+/* -*- Mode: c++; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
+ * 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/. */
+
+#ifndef PrefsHelper_h
+#define PrefsHelper_h
+
+#include "GeneratedJNINatives.h"
+#include "MainThreadUtils.h"
+#include "nsAppShell.h"
+
+#include "mozilla/UniquePtr.h"
+
+namespace mozilla {
+
+struct PrefsHelper
+    : widget::PrefsHelper::Natives<PrefsHelper>
+    , UsesGeckoThreadProxy
+{
+    PrefsHelper() = delete;
+
+    static void GetPrefsById(const jni::ClassObject::LocalRef& cls,
+                             int32_t requestId,
+                             jni::ObjectArray::Param prefNames,
+                             bool observe)
+    {
+        MOZ_ASSERT(NS_IsMainThread());
+        MOZ_ASSERT(nsAppShell::gAppShell);
+
+        nsTArray<jni::Object::LocalRef> namesRefArray(prefNames.GetElements());
+        const size_t len = namesRefArray.Length();
+
+        // Java strings are not null-terminated, but XPCOM expects
+        // null-terminated strings, so we copy the strings to nsString to
+        // ensure null-termination.
+        nsTArray<nsString> namesStrArray(len);
+        nsTArray<const char16_t*> namesPtrArray(len);
+
+        for (size_t i = 0; i < len; i++) {
+            if (!namesRefArray[i]) {
+                namesPtrArray.AppendElement(nullptr);
+                continue;
+            }
+            namesPtrArray.AppendElement(namesStrArray.AppendElement(
+                    nsString(jni::String::LocalRef(
+                    mozilla::Move(namesRefArray[i]))))->Data());
+        }
+
+        nsIAndroidBrowserApp* browserApp = nullptr;
+        nsAppShell::gAppShell->GetBrowserApp(&browserApp);
+        MOZ_ASSERT(browserApp);
+
+        if (observe) {
+            browserApp->ObservePreferences(
+                    requestId, len ? &namesPtrArray[0] : nullptr, len);
+        } else {
+            browserApp->GetPreferences(
+                    requestId, len ? &namesPtrArray[0] : nullptr, len);
+        }
+    }
+
+    static void RemovePrefsObserver(int32_t requestId)
+    {
+        MOZ_ASSERT(NS_IsMainThread());
+        MOZ_ASSERT(nsAppShell::gAppShell);
+
+        nsIAndroidBrowserApp* browserApp = nullptr;
+        nsAppShell::gAppShell->GetBrowserApp(&browserApp);
+        MOZ_ASSERT(browserApp);
+
+        browserApp->RemovePreferenceObservers(requestId);
+    }
+};
+
+} // namespace
+
+#endif // PrefsHelper_h

widget/android/nsAppShell.cpp

@@ -60,6 +60,7 @@
 #endif
 
 #include "ANRReporter.h"
+#include "PrefsHelper.h"
 
 #ifdef DEBUG_ANDROID_EVENTS
 #define EVLOG(args...)  ALOG(args)
@@ -195,6 +196,7 @@ nsAppShell::nsAppShell()
         AndroidBridge::ConstructBridge();
         GeckoThreadNatives::Init();
         mozilla::ANRReporter::Init();
+        mozilla::PrefsHelper::Init();
         nsWindow::InitNatives();
 
         widget::GeckoThread::SetState(widget::GeckoThread::State::JNI_READY());