Use new hide panel icon

Fixes #8018

src/vs/workbench/browser/parts/panel/media/hide-inverse.svg

+<?xml version="1.0" encoding="utf-8"?>
+<!-- Generator: Adobe Illustrator 19.2.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
+<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
+	 viewBox="0 0 16 16" style="enable-background:new 0 0 16 16;" xml:space="preserve">
+<style type="text/css">
+	.st0{fill:#C5C5C5;}
+</style>
+<path id="iconBg" class="st0" d="M8,11.3L2.1,5.4l0.7-0.7L8,9.9l5.1-5.1l0.7,0.7C13.9,5.4,8,11.3,8,11.3z"/>
+</svg>

src/vs/workbench/browser/parts/panel/media/hide.svg

+<?xml version="1.0" encoding="utf-8"?>
+<!-- Generator: Adobe Illustrator 19.2.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
+<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
+	 viewBox="0 0 16 16" style="enable-background:new 0 0 16 16;" xml:space="preserve">
+<style type="text/css">
+	.st0{fill:#424242;}
+</style>
+<path id="iconBg" class="st0" d="M8,11.3L2.1,5.4l0.7-0.7L8,9.9l5.1-5.1l0.7,0.7C13.9,5.4,8,11.3,8,11.3z"/>
+</svg>

src/vs/workbench/browser/parts/panel/media/panelpart.css

@@ -15,7 +15,29 @@
 	z-index: initial;
 }
 
+.monaco-workbench .hide-panel-action {
+	background: url('hide.svg') center center no-repeat;
+}
+
+.vs-dark .monaco-workbench .hide-panel-action {
+	background: url('hide-inverse.svg') center center no-repeat;
+}
+
 /* High Contrast Theming */
 .hc-black .monaco-workbench > .part.panel > .title {
 	border-top-color: #6FC3DF;
 }
+
+.hc-black .monaco-workbench .hide-panel-action {
+	background: none;
+}
+
+.hc-black .monaco-workbench .hide-panel-action:before {
+	content: url('hide-inverse.svg');
+	position: absolute;
+	top: 12px;
+	left: 8px;
+	height: 16px;
+	width: 16px;
+}
+

src/vs/workbench/browser/parts/panel/panelPart.ts

@@ -120,7 +120,7 @@ class ClosePanelAction extends Action {
 		name: string,
 		@IPartService private partService: IPartService
 	) {
-		super(id, name, 'close-editor-action');
+		super(id, name, 'hide-panel-action');
 	}
 
 	public run(): TPromise<boolean> {