Abstract ZygoteInit.maybePreload call for webview.

Make ZygoteConnection call ZygoteInit.maybePreload via an overridable
method on itself, so that the WebView zygote's subclass of
ZygoteConnection can override it to do nothing; the WebView zygote
doesn't want to do this preloading and can't due to permissions.

Test: enable multiprocess webview, test webview apps work
Bug: 32735001
Change-Id: Ia6ac7d35172ba69ff861fe5a44b09ac52b0afbf0

core/java/com/android/internal/os/WebViewZygoteInit.java

@@ -53,6 +53,11 @@ class WebViewZygoteInit {
             super(socket, abiList);
         }
 
+        @Override
+        protected void maybePreload() {
+            // Do nothing, we don't need to call ZygoteInit.maybePreload() for the WebView zygote.
+        }
+
         @Override
         protected boolean handlePreloadPackage(String packagePath, String libsPath) {
             // Ask ApplicationLoaders to create and cache a classloader for the WebView APK so that

core/java/com/android/internal/os/ZygoteConnection.java

@@ -171,7 +171,7 @@ class ZygoteConnection {
                 return handleAbiListQuery();
             }
 
-            ZygoteInit.maybePreload();
+            maybePreload();
 
             if (parsedArgs.preloadPackage != null) {
                 return handlePreloadPackage(parsedArgs.preloadPackage,
@@ -279,6 +279,10 @@ class ZygoteConnection {
         }
     }
 
+    protected void maybePreload() {
+        ZygoteInit.maybePreload();
+    }
+
     protected boolean handlePreloadPackage(String packagePath, String libsPath) {
         throw new RuntimeException("Zyogte does not support package preloading");
     }