DevTools: draw realistic chrome on top of viewport in layers3dview

- add graphics for chrome on top of viewport rectange;
- make viewport border light-grey, let its width scale along with
    contents scale.
- change Viewport checkbox to Chrome (always show viewport)
- (drive by) properly handle potential image/texture creation errors
- (drive by) disable user selection on Layers3DView in CSS as annoying.

BUG=

Review URL: https://codereview.chromium.org/661753002

git-svn-id: svn://svn.chromium.org/blink/trunk@183906 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/devtools/devtools.gypi

@@ -600,6 +600,9 @@
             'front_end/Images/cookie.png',
             'front_end/Images/chromeDisabledSelect.png',
             'front_end/Images/chromeDisabledSelect_2x.png',
+            'front_end/Images/chromeLeft.png',
+            'front_end/Images/chromeMiddle.png',
+            'front_end/Images/chromeRight.png',
             'front_end/Images/chromeSelect.png',
             'front_end/Images/chromeSelect_2x.png',
             'front_end/Images/database.png',

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

@@ -746,6 +746,7 @@
 
 .layers-3d-view {
     overflow: hidden;
+    -webkit-user-select: none;
 }
 
 .layers-3d-view canvas {