Bug 1533425 - Look for architecture-specific greprefs.js files on Android r=njn

We want to publish a multi-architecture AAR for GeckoView which includes
a single omni.ja, but we archicture-specific changes in greprefs.js that
prevent this from working. This patch causes us to try to read an
architecture-specific greprefs.js first, which will be provided by the
packaging process for the fat AAR.

Differential Revision: https://phabricator.services.mozilla.com/D22526

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

mobile/android/geckoview/src/main/java/org/mozilla/gecko/mozglue/GeckoLoader.java

@@ -116,6 +116,7 @@ public final class GeckoLoader {
         }
     }
 
+    @SuppressWarnings("deprecation") // for Build.CPU_ABI
     public synchronized static void setupGeckoEnvironment(final Context context,
                                                           final String profilePath,
                                                           final Collection<String> env,
@@ -176,6 +177,7 @@ public final class GeckoLoader {
         }
 
         putenv("MOZ_ANDROID_DEVICE_SDK_VERSION=" + Build.VERSION.SDK_INT);
+        putenv("MOZ_ANDROID_CPU_ABI=" + Build.CPU_ABI);
 
         setupInitialPrefs(prefs);
 

modules/libpref/Preferences.cpp

@@ -4418,7 +4418,7 @@ float MOZ_MAYBE_UNUSED GetPref<float>(const char* aName, float aDefaultValue) {
   // Thus, in the omni.jar case, we always load app-specific default
   // preferences from omni.jar, whether or not `$app == $gre`.
 
-  nsresult rv;
+  nsresult rv = NS_ERROR_FAILURE;
   nsZipFind* findPtr;
   nsAutoPtr<nsZipFind> find;
   nsTArray<nsCString> prefEntries;
@@ -4428,8 +4428,24 @@ float MOZ_MAYBE_UNUSED GetPref<float>(const char* aName, float aDefaultValue) {
   RefPtr<nsZipArchive> jarReader =
       mozilla::Omnijar::GetReader(mozilla::Omnijar::GRE);
   if (jarReader) {
+#ifdef MOZ_WIDGET_ANDROID
+    // Try to load an architecture-specific greprefs.js first. This will be
+    // present in FAT AAR builds of GeckoView on Android.
+    const char* abi = getenv("MOZ_ANDROID_CPU_ABI");
+    if (abi) {
+      nsAutoCString path;
+      path.AppendPrintf("%s/greprefs.js", abi);
+      rv = pref_ReadPrefFromJar(jarReader, path.get());
+    }
+
+    if (NS_FAILED(rv)) {
+      // Fallback to toplevel greprefs.js if arch-specific load fails.
+      rv = pref_ReadPrefFromJar(jarReader, "greprefs.js");
+    }
+#else
     // Load jar:$gre/omni.jar!/greprefs.js.
     rv = pref_ReadPrefFromJar(jarReader, "greprefs.js");
+#endif
     NS_ENSURE_SUCCESS(rv, Err("pref_ReadPrefFromJar() failed"));
 
     // Load jar:$gre/omni.jar!/defaults/pref/*.js.