Used cached doc position in getLayoutRect.

src/service/viewport-impl.js

@@ -244,7 +244,8 @@ export class Viewport {
    * @return {!LayoutRect}
    */
   getLayoutRect(el) {
-    return this.binding_.getLayoutRect(el);
+    return this.binding_.getLayoutRect(el,
+        this.getScrollLeft(), this.getScrollTop());
   }
 
   /**
@@ -577,9 +578,13 @@ class ViewportBindingDef {
   /**
    * Returns the rect of the element within the document.
    * @param {!Element} unusedEl
+   * @param {number=} unusedScrollLeft Optional arguments that the caller may
+   *     pass in, if they cached these values and would like to avoid
+   *     remeasure. Requires appropriate updating the values on scroll.
+   * @param {number=} unusedScrollTop Same comment as above.
    * @return {!LayoutRect}
    */
-  getLayoutRect(unusedEl) {}
+  getLayoutRect(unusedEl, unusedScrollLeft, unusedScrollTop) {}
 
   /** For testing. */
   cleanup_() {}
@@ -686,9 +691,13 @@ export class ViewportBindingNatural_ {
   }
 
   /** @override */
-  getLayoutRect(el) {
-    const scrollTop = this.getScrollTop();
-    const scrollLeft = this.getScrollLeft();
+  getLayoutRect(el, opt_scrollLeft, opt_scrollTop) {
+    const scrollTop = opt_scrollTop != undefined
+        ? opt_scrollTop
+        : this.getScrollTop();
+    const scrollLeft = opt_scrollLeft != undefined
+        ? opt_scrollLeft
+        : this.getScrollLeft();
     const b = el./*OK*/getBoundingClientRect();
     return layoutRectLtwh(Math.round(b.left + scrollLeft),
         Math.round(b.top + scrollTop),

test/functional/test-viewport.js

@@ -218,6 +218,16 @@ describe('Viewport', () => {
     viewport.scrollIntoView(element);
   });
 
+  it('should send cached scroll pos to getLayoutRect', () => {
+    const element = document.createElement('div');
+    const bindingMock = sandbox.mock(binding);
+    viewport.scrollTop_ = 111;
+    viewport.scrollLeft_ = 222;
+    bindingMock.expects('getLayoutRect').withArgs(element, 222, 111)
+        .returns('sentinel').once();
+    expect(viewport.getLayoutRect(element)).to.equal('sentinel');
+  });
+
   it('should deletegate scrollWidth', () => {
     const bindingMock = sandbox.mock(binding);
     bindingMock.expects('getScrollWidth').withArgs().returns(111).once();
@@ -601,6 +611,22 @@ describe('ViewportBindingNatural', () => {
     expect(rect.width).to.equal(14);  // round(13.5)
     expect(rect.height).to.equal(15);  // round(14.5)
   });
+
+  it('should offset client rect for layout and position passed in', () => {
+    windowApi.pageXOffset = 1000;
+    windowApi.pageYOffset = 2000;
+    windowApi.document = {scrollingElement: {}};
+    const el = {
+      getBoundingClientRect: () => {
+        return {left: 11.5, top: 12.5, width: 13.5, height: 14.5};
+      },
+    };
+    const rect = binding.getLayoutRect(el, 100, 200);
+    expect(rect.left).to.equal(112);  // round(100 + 11.5)
+    expect(rect.top).to.equal(213);  // round(200 + 12.5)
+    expect(rect.width).to.equal(14);  // round(13.5)
+    expect(rect.height).to.equal(15);  // round(14.5)
+  });
 });