DevTools: promote large views with overflow to layers in order to not repaint on scroll.

Review URL: https://codereview.chromium.org/205193002

git-svn-id: svn://svn.chromium.org/blink/trunk@169792 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/devtools/front_end/dataGrid.css

@@ -28,6 +28,7 @@
     right: 0;
     overflow-x: hidden;
     overflow-y: overlay;
+    -webkit-transform: translateZ(0);
 }
 
 .data-grid.inline {

third_party/WebKit/Source/devtools/front_end/elementsPanel.css

@@ -31,6 +31,7 @@
     flex: 1 1;
     overflow: auto;
     padding-left: 0;
+    -webkit-transform: translateZ(0);
 }
 
 #elements-crumbs {
@@ -43,6 +44,7 @@
 #elements-content > ol {
     display: inline-block;
     min-height: 100%;
+    -webkit-transform: translateZ(0);
 }
 
 #elements-content .editing {
@@ -567,7 +569,6 @@
 }
 
 .sidebar-pane.composite {
-    overflow: hidden;
     position: absolute;
 }
 

third_party/WebKit/Source/devtools/front_end/navigatorView.css

@@ -102,10 +102,12 @@
 
 .navigator-tabbed-pane .navigator-container {
     overflow: auto;
+    -webkit-transform: translateZ(0);
 }
 
 .navigator-tabbed-pane .navigator {
     padding-left: 0;
+    -webkit-transform: translateZ(0);
 }
 
 .navigator-tabbed-pane .tabbed-pane-header-contents {

third_party/WebKit/Source/devtools/front_end/sidebarPane.css

@@ -34,8 +34,6 @@
 .sidebar-pane > .body {
     position: relative;
     display: none;
-    overflow-y: auto;
-    overflow-x: hidden;
 }
 
 .sidebar-pane > .body .info {