Fix occasional squared left tab edge at 150% scale

I don't (yet) know why this fixes the issue, but it certainly does. This
diff *should* be a no-op, changing an rLineTo to the equivalent lineTo,
but I guess the former runs into a bug in skia.

Stepping through this in the debugger reveals that there is some
floating-point error in the path's point sequence that the rLineTo
propagates and the lineTo obviously does not.  Apparently 0.5000015259
vs. 0.5 or 53.0000038 vs 53 makes a difference to skia when it's
calculating the path intersection.  ¯\_(ツ)_/¯

Bug: 864280
Change-Id: I06ba430f7f62f075102975e1e3db4b8a3292c879
Reviewed-on: https://chromium-review.googlesource.com/1141292Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Taylor Bergquist <tbergquist@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577233}

chrome/browser/ui/views/tabs/tab.cc

@@ -272,7 +272,7 @@ gfx::Path GetRefreshInteriorPath(float scale,
   // Bottom left.
   left_path.arcTo(radius, radius, 0, SkPath::kSmall_ArcSize,
                   SkPath::kCW_Direction, left + corner_gap, bottom);
-  left_path.rLineTo(0, bottom_extension);
+  left_path.lineTo(left + corner_gap, extended_bottom);
 
   // Bottom/top edges of left side.
   left_path.lineTo(right, extended_bottom);