Update most LayoutTests to be agnostic to scrollTopLeftInterop mode

LayoutTests/fast/scroll-behavior/main-frame-element-scrollBy.html

Index: LayoutTests/fast/scroll-behavior/main-frame-element-scrollBy.html
diff --git a/LayoutTests/fast/scroll-behavior/main-frame-element-scrollBy.html b/LayoutTests/fast/scroll-behavior/main-frame-element-scrollBy.html
index c27a57c8de4629aa4466e82056dd437ba29d4109..37105b6144dd8545a5bf8d5061e9c9c290db830e 100644
--- a/LayoutTests/fast/scroll-behavior/main-frame-element-scrollBy.html
+++ b/LayoutTests/fast/scroll-behavior/main-frame-element-scrollBy.html
@@ -33,9 +33,9 @@
           scrollToOptions.left = testCase.x;
         if (testCase.y)
           scrollToOptions.top = testCase.y;
-        document.body.scrollBy(scrollToOptions);
+        document.scrollingElement.scrollBy(scrollToOptions);
       } else {
-        document.body.scrollBy(testCase.x, testCase.y);
+        document.scrollingElement.scrollBy(testCase.x, testCase.y);
       }
     }
 
@@ -66,7 +66,7 @@
         testCases.push(new ScrollBehaviorTestCase(testScrolls[i]));
       }
 
-      var scrollBehaviorTest = new ScrollBehaviorTest(document.body,
+      var scrollBehaviorTest = new ScrollBehaviorTest(document.scrollingElement,
                                                       document,
                                                       testCases,
                                                       getEndPosition,