Allow switching to the Chromium WebViewFactoryProvider at runtime.

Currently, WebViewFactory is hardcoded to always load
android.webkit.WebViewClassic$Factory.  This change allows us to
load the Chromium powered WebView by setting the
"webview.use_chromium" system propery to true.

Change-Id: Icebfc4d5c4a61230c5e5dccac1ec5eca59f650ac

Author: Ben Murdoch

core/java/android/webkit/WebViewFactory.java

@@ -16,14 +16,23 @@
 
 package android.webkit;
 
+import android.os.Build;
+import android.os.StrictMode;
+import android.os.SystemProperties;
 import android.util.Log;
 
+import dalvik.system.PathClassLoader;
+
 /**
  * Top level factory, used creating all the main WebView implementation classes.
  */
 class WebViewFactory {
     // Default Provider factory class name.
-    private static final String DEFAULT_WEB_VIEW_FACTORY = "android.webkit.WebViewClassic$Factory";
+    // TODO: When the Chromium powered WebView is ready, it should be the default factory class.
+    private static final String DEFAULT_WEBVIEW_FACTORY = "android.webkit.WebViewClassic$Factory";
+    private static final String CHROMIUM_WEBVIEW_FACTORY =
+            "com.android.webviewchromium.WebViewChromiumFactoryProvider";
+    private static final String CHROMIUM_WEBVIEW_JAR = "/system/framework/webviewchromium.jar";
 
     private static final String LOGTAG = "WebViewFactory";
 
@@ -38,18 +47,45 @@ static synchronized WebViewFactoryProvider getProvider() {
         // us honest and minimize usage of WebViewClassic internals when binding the proxy.
         if (sProviderInstance != null) return sProviderInstance;
 
-        sProviderInstance = getFactoryByName(DEFAULT_WEB_VIEW_FACTORY);
+        // For debug builds, we allow a system property to specify that we should use the
+        // Chromium powered WebView. This enables us to switch between implementations
+        // at runtime. For user (release) builds, don't allow this.
+        if (Build.IS_DEBUGGABLE && SystemProperties.getBoolean("webview.use_chromium", false)) {
+            StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskReads();
+            try {
+                sProviderInstance = loadChromiumProvider();
+                if (DEBUG) Log.v(LOGTAG, "Loaded Chromium provider: " + sProviderInstance);
+            } finally {
+                StrictMode.setThreadPolicy(oldPolicy);
+            }
+        }
+
         if (sProviderInstance == null) {
-            if (DEBUG) Log.v(LOGTAG, "Falling back to explicit linkage");
-            sProviderInstance = new WebViewClassic.Factory();
+            if (DEBUG) Log.v(LOGTAG, "Falling back to default provider: "
+                    + DEFAULT_WEBVIEW_FACTORY);
+            sProviderInstance = getFactoryByName(DEFAULT_WEBVIEW_FACTORY,
+                    WebViewFactory.class.getClassLoader());
+            if (sProviderInstance == null) {
+                if (DEBUG) Log.v(LOGTAG, "Falling back to explicit linkage");
+                sProviderInstance = new WebViewClassic.Factory();
+            }
         }
         return sProviderInstance;
     }
 
-    private static WebViewFactoryProvider getFactoryByName(String providerName) {
+    // TODO: This allows us to have the legacy and Chromium WebView coexist for development
+    // and side-by-side testing. After transition, remove this when no longer required.
+    private static WebViewFactoryProvider loadChromiumProvider() {
+        ClassLoader clazzLoader = new PathClassLoader(CHROMIUM_WEBVIEW_JAR, null,
+                WebViewFactory.class.getClassLoader());
+        return getFactoryByName(CHROMIUM_WEBVIEW_FACTORY, clazzLoader);
+    }
+
+    private static WebViewFactoryProvider getFactoryByName(String providerName,
+            ClassLoader loader) {
         try {
             if (DEBUG) Log.v(LOGTAG, "attempt to load class " + providerName);
-            Class<?> c = Class.forName(providerName);
+            Class<?> c = Class.forName(providerName, true, loader);
             if (DEBUG) Log.v(LOGTAG, "instantiating factory");
             return (WebViewFactoryProvider) c.newInstance();
         } catch (ClassNotFoundException e) {