Add observers for DIP scale change.

content/browser/site_per_process_browsertest.cc

 // 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.
 
 #include "content/browser/site_per_process_browsertest.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 608 matching lines @@
                                             &device_scale_factor));
   return device_scale_factor;
 }
 
 IN_PROC_BROWSER_TEST_F(SitePerProcessHighDPIBrowserTest,
                        SubframeLoadsWithCorrectDeviceScaleFactor) {
   GURL main_url(embedded_test_server()->GetURL(
       "a.com", "/cross_site_iframe_factory.html?a(b)"));
   NavigateToURL(shell(), main_url);
 
-  EXPECT_EQ(SitePerProcessHighDPIBrowserTest::kDeviceScaleFactor,
-            GetFrameDeviceScaleFactor(web_contents()));
+  // On Android forcing device scale factor does not work for tests, therefore
+  // we ensure that make frame and iframe have the same DIP scale there, but
+  // not necessarily kDeviceScaleFactor.
+  const double expected_dip_scale =
+#if defined(OS_ANDROID)
+      GetFrameDeviceScaleFactor(web_contents());
+#else
+      SitePerProcessHighDPIBrowserTest::kDeviceScaleFactor;
+#endif
+
+  EXPECT_EQ(expected_dip_scale, GetFrameDeviceScaleFactor(web_contents()));
 
   FrameTreeNode* root = web_contents()->GetFrameTree()->root();
+  ASSERT_EQ(1U, root->child_count());
+
   FrameTreeNode* child = root->child_at(0);
-  EXPECT_EQ(SitePerProcessHighDPIBrowserTest::kDeviceScaleFactor,
-            GetFrameDeviceScaleFactor(child));
+  EXPECT_EQ(expected_dip_scale, GetFrameDeviceScaleFactor(child));
 }
 
 // Ensure that navigating subframes in --site-per-process mode works and the
 // correct documents are committed.
 #if defined(OS_WIN)
 // This test is flaky on Windows, see https://crbug.com/629419.
 #define MAYBE_CrossSiteIframe DISABLED_CrossSiteIframe
 #else
 #define MAYBE_CrossSiteIframe CrossSiteIframe
 #endif
@@ skipping 7880 matching lines @@
   EXPECT_TRUE(NavigateToURL(shell(), b_url));
 
   base::string16 expected_title(base::UTF8ToUTF16("foo"));
   TitleWatcher title_watcher(popup2->web_contents(), expected_title);
   EXPECT_TRUE(ExecuteScript(
       shell(), "window.open('','popup2').postMessage('foo', '*');"));
   EXPECT_EQ(expected_title, title_watcher.WaitAndGetTitle());
 }
 
 }  // namespace content