Bug 1430918 - Draw grid outline from origin. r=gl

The transforms that can be applied to the grid outline to adjust for writing
mode may include translation and reflection based on the outline's width or
height.  To achieve the expected result, we need to start drawing the outline at
(0, 0) instead of (1, 1).

MozReview-Commit-ID: HjbREuyNpvH

--HG--
extra : rebase_source : c8dadf60f7d4d4ee9763e29fb6d1ab878beb5afd

devtools/client/inspector/grids/components/GridOutline.js

@@ -219,8 +219,8 @@ class GridOutline extends PureComponent {
     const numberOfColumns = cols.lines.length - 1;
     const numberOfRows = rows.lines.length - 1;
     const rectangles = [];
-    let x = 1;
-    let y = 1;
+    let x = 0;
+    let y = 0;
     let width = 0;
     let height = 0;
 
@@ -240,7 +240,7 @@ class GridOutline extends PureComponent {
         x += width;
       }
 
-      x = 1;
+      x = 0;
       y += height;
     }
 
@@ -315,8 +315,8 @@ class GridOutline extends PureComponent {
       {
         key: "border",
         className: "grid-outline-border",
-        x: 1,
-        y: 1,
+        x: 0,
+        y: 0,
         width: borderWidth,
         height: borderHeight
       }