Update SVG tests ahead of offset* removal

third_party/WebKit/LayoutTests/svg/custom/size-follows-container-size.html

Index: third_party/WebKit/LayoutTests/svg/custom/size-follows-container-size.html
diff --git a/third_party/WebKit/LayoutTests/svg/custom/size-follows-container-size.html b/third_party/WebKit/LayoutTests/svg/custom/size-follows-container-size.html
index eaa8c0d82fcb9cfbdb39d32b896d69f629ef5161..3ae86c3956b105f325f0169f98b4d74d7f854489 100644
--- a/third_party/WebKit/LayoutTests/svg/custom/size-follows-container-size.html
+++ b/third_party/WebKit/LayoutTests/svg/custom/size-follows-container-size.html
@@ -15,14 +15,16 @@
         requestAnimationFrame(function() {
             document.querySelector('div').style.width = "1000px";
             inc_test.step(function() {
-                assert_equals(document.querySelector('svg').offsetWidth, 1000);
-                assert_equals(document.querySelector('svg').offsetHeight, 1000);
+                var rect = document.querySelector('svg').getBoundingClientRect();
+                assert_equals(rect.width, 1000);
+                assert_equals(rect.height, 1000);
             });
             inc_test.done();
             document.querySelector('div').style.width = "100px";
             dec_test.step(function() {
-                assert_equals(document.querySelector('svg').offsetWidth, 100);
-                assert_equals(document.querySelector('svg').offsetHeight, 100);
+                var rect = document.querySelector('svg').getBoundingClientRect();
+                assert_equals(rect.width, 100);
+                assert_equals(rect.height, 100);
             });
             dec_test.done();
         });