fix(grid-list): avoid unnecessary calc declarations (#6745)

For the cases where a tile's offset is 0, some of the `calc` expressions will always evaluate to 0. These changes make it so calc isn't used at all if it would evaluate to 0.

src/lib/grid-list/grid-list.spec.ts

@@ -253,6 +253,18 @@ describe('MdGridList', () => {
     let footer = fixture.debugElement.query(By.directive(MdGridTileText));
     expect(footer.nativeElement.classList.contains('mat-2-line')).toBe(true);
   });
+
+  it('should not use calc() that evaluates to 0', () => {
+    const fixture = TestBed.createComponent(GirdListWithRowHeightRatio);
+
+    fixture.componentInstance.heightRatio = '4:1';
+    fixture.detectChanges();
+
+    const firstTile = fixture.debugElement.query(By.directive(MdGridTile)).nativeElement;
+
+    expect(firstTile.style.marginTop).toBe('0px');
+    expect(firstTile.style.left).toBe('0px');
+  });
 });
 
 

src/lib/grid-list/tile-styler.ts

@@ -51,7 +51,7 @@ export abstract class TileStyler {
     // edges, each tile only uses a fraction (gutterShare = numGutters / numCells) of the gutter
     // size. (Imagine having one gutter per tile, and then breaking up the extra gutter on the
     // edge evenly among the cells).
-    return `(${sizePercent}% - ( ${this._gutterSize} * ${gutterFraction} ))`;
+    return `(${sizePercent}% - (${this._gutterSize} * ${gutterFraction}))`;
   }
 
 
@@ -64,7 +64,7 @@ export abstract class TileStyler {
   getTilePosition(baseSize: string, offset: number): string {
     // The position comes the size of a 1x1 tile plus gutter for each previous tile in the
     // row/column (offset).
-    return calc(`(${baseSize} + ${this._gutterSize}) * ${offset}`);
+    return offset === 0 ? '0' : calc(`(${baseSize} + ${this._gutterSize}) * ${offset}`);
   }