Initialize device scale factor correctly on Android

content/public/android/javatests/src/org/chromium/content/browser/ViewportTest.java

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.content.browser;
+
+import android.content.Context;
+import android.test.suitebuilder.annotation.MediumTest;
+import android.util.DisplayMetrics;
+import android.view.Display;
+import android.view.WindowManager;
+
+import org.chromium.base.test.util.Feature;
+import org.chromium.content.browser.test.util.JavaScriptUtils;
+import org.chromium.content.browser.test.util.TestCallbackHelperContainer;
+import org.chromium.content.common.DeviceInfo;
+
+/**
+ * Test suite for viewport-related properties.
+ */
+public class ViewportTest extends ContentViewTestBase {
+
+    private TestCallbackHelperContainer mCallbackHelper;
+
+    /**
+     * Returns the TestCallbackHelperContainer associated with this ContentView,
+     * or creates it lazily.
+     */
+    protected TestCallbackHelperContainer getTestCallbackHelperContainer() {
+        if (mCallbackHelper == null) {
+            mCallbackHelper = new TestCallbackHelperContainer(getContentView());
+        }
+        return mCallbackHelper;
+    }
+
+    protected String evaluateStringValue(String expression) throws Throwable {
+        return JavaScriptUtils.executeJavaScriptAndWaitForResult(this, getContentView(),
+                getTestCallbackHelperContainer(), expression);
+    }
+
+    protected float evaluateFloatValue(String expression) throws Throwable {
+        return Float.valueOf(evaluateStringValue(expression));
+    }
+
+    protected int evaluateIntegerValue(String expression) throws Throwable {
+        return Integer.valueOf(evaluateStringValue(expression));
+    }
+
+    @MediumTest
+    @Feature({"Viewport", "InitialViewportSize"})
+    public void testDefaultViewportSize() throws Throwable {
+        launchContentShellWithUrl("about:blank");
+        waitForActiveShellToBeDoneLoading();
+
+        Context context = getInstrumentation().getTargetContext();
+        WindowManager winManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
+        DisplayMetrics metrics = new DisplayMetrics();
+        winManager.getDefaultDisplay().getMetrics(metrics);
+
+        // window.devicePixelRatio should match the default display. Only check to 1 decimal place
+        // to allow for rounding.
+        assertEquals(String.format("%.1g", metrics.density),
+                String.format("%.1g", evaluateFloatValue("window.devicePixelRatio")));
+
+        // Check that the viewport width is vaguely sensible.
+        int viewportWidth = evaluateIntegerValue("document.documentElement.clientWidth");
+        assertTrue(Math.abs(evaluateIntegerValue("window.innerWidth") - viewportWidth) <= 1);
+        assertTrue(viewportWidth >= 979);
+        assertTrue(viewportWidth <= Math.max(981, metrics.widthPixels / metrics.density + 1));
+    }
+}