Revert of DevTools: Correct Source Panel Show/Hide Toolbar buttons (patchset #1 id:1 of https://codereview.chromium.org/2600493002/ )

Reason for revert:
It turned out the icons are actually wrong. Compare:
- Without this patch (correct): http://imgur.com/a/eFCnz
- With this patch (incorrect): http://imgur.com/a/gJ24q

Original issue's description:
> DevTools: Correct Source Panel Show/Hide Toolbar buttons
>
> Regression : Misalignment of 'Hide Navigator' and 'Hide Debugger' buttons is seen in devtools.
>
> Flipped mask positions and removed—now unnecessary—rotation transforms around show/hide panel icon containers.
>
> BUG=671930
> R=lushnikov@chromium.org
> TEST=Open Dev Tools, open Sources Pane, observe show/hide sidebar buttons
> are correctly aligned. crbug.com/671930
>
> Review-Url: https://codereview.chromium.org/2600493002
> Cr-Commit-Position: refs/heads/master@{#445339}
> Committed: https://chromium.googlesource.com/chromium/src/+/4d2364eb32a5b242790324536efccd843cb81aa8

TBR=dgozman@chromium.org,pfeldman@chromium.org,me@jakehendy.com
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=671930

Review-Url: https://codereview.chromium.org/2655793003
Cr-Commit-Position: refs/heads/master@{#445983}

Author: aslushnikov

front_end/ui/Icon.js

@@ -170,8 +170,10 @@ UI.Icon.Descriptors = {
 
   'largeicon-show-left-sidebar': {x: -160, y: -72, width: 28, height: 24, spritesheet: 'largeicons', isMask: true},
   'largeicon-hide-left-sidebar': {x: -192, y: -72, width: 28, height: 24, spritesheet: 'largeicons', isMask: true},
-  'largeicon-show-right-sidebar': {x: -192, y: -72, width: 28, height: 24, spritesheet: 'largeicons', isMask: true},
-  'largeicon-hide-right-sidebar': {x: -160, y: -72, width: 28, height: 24, spritesheet: 'largeicons', isMask: true},
+  'largeicon-show-right-sidebar':
+      {x: -160, y: -72, width: 28, height: 24, spritesheet: 'largeicons', isMask: true, transform: 'rotate(180deg)'},
+  'largeicon-hide-right-sidebar':
+      {x: -192, y: -72, width: 28, height: 24, spritesheet: 'largeicons', isMask: true, transform: 'rotate(180deg)'},
   'largeicon-show-top-sidebar': {
     x: -160,
     y: -72,