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 4 decimal places

[johnme, 2012/10/30 14:38:23]

I might only check to 1dp. For example anywhere in the range 1.33 to 1.35 is
reasonable for Nexus 7.

[Sami, 2012/10/31 11:12:57]

Good point. Done.

+        // to allow for rounding.
+        assertEquals(String.format("%.4g", metrics.density),
+                String.format("%.4g", evaluateFloatValue("window.devicePixelRatio")));
+
+        // Screen size should match the default display.

[johnme, 2012/10/30 14:38:23]

That's not necessarily true. Beverloo and I think this should return logical UI
pixels (i.e. size in physical screen pixels divided by devicePixelRatio). It
seems that would also match what Apple do:
http://stackoverflow.com/questions/4833669/iphone-4-screen-width-reports-320-...

In the meantime, I'm not sure how useful it is to test this.

[Sami, 2012/10/31 11:12:57]

That sounds like a different bug. I'll just remove this part of the test.

+        assertEquals(metrics.widthPixels, evaluateIntegerValue("screen.width"));
+        assertEquals(metrics.heightPixels, evaluateIntegerValue("screen.height"));
+
+        // FIXME: We should check the exact expected values for inner and outer sizes, but for
+        // now we only ensure they are not the same with a non-identity device pixel ratio.

[johnme, 2012/10/30 14:38:23]

It's not clear why you expect them to be different; indeed while they usually
will be, on a 980 screen pixel wide device they should be equal. I think it
would be better to check that:

    eval(window.outerWidth) ~= metrics.widthPixels / metrics.density

and

    eval(window.innerWidth) == eval(document.documentElement.clientWidth) == 980

[Sami, 2012/10/31 11:12:57]

I've replaced this with the test we designed offline.

+        if (metrics.density != 1) {
+            assertFalse(evaluateIntegerValue("window.innerWidth") ==
+                    evaluateIntegerValue("window.outerWidth"));
+            assertFalse(evaluateIntegerValue("window.innerHeight") ==
+                    evaluateIntegerValue("window.outerHeight"));
+        }
+    }
+}