Revert of DevTools: Add dark theme hidden experiment (patchset #2 id:20001 of...

Revert of DevTools: Add dark theme hidden experiment (patchset #2 id:20001 of https://codereview.chromium.org/1458223005/ )

Reason for revert:
Since the theme does not work and can't be used, this should really be behind 10 shifts.

Original issue's description:
> DevTools: Add dark theme hidden experiment
>
> BUG=559524
>
> Committed: https://crrev.com/a7d0f43f83b514a46ec3850aab3160412cdd8a53
> Cr-Commit-Position: refs/heads/master@{#361015}

TBR=paulirish@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=559524

Review URL: https://codereview.chromium.org/1471693003

Cr-Commit-Position: refs/heads/master@{#361174}

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

@@ -46,10 +46,6 @@ body {
     color: #222;
 }
 
-body.dark-theme {
-    -webkit-filter: invert(100%) hue-rotate(180deg) saturate(80%);
-}
-
 .platform-linux {
     color: rgb(48, 57, 66);
     font-family: Ubuntu, Arial, sans-serif;
@@ -558,10 +554,6 @@ body.inactive .sidebar-tree-item.selected {
     bottom: 0;
 }
 
-body.dark-theme .root-view {
-    background: white;
-}
-
 .viewport-control-gap-element {
     color: transparent;
 }

third_party/WebKit/Source/devtools/front_end/main/Main.js

@@ -107,7 +107,6 @@ WebInspector.Main.prototype = {
         Runtime.experiments.register("applyCustomStylesheet", "Allow custom UI themes");
         Runtime.experiments.register("blackboxJSFramesOnTimeline", "Blackbox JavaScript frames on Timeline", true);
         Runtime.experiments.register("colorContrastRatio", "Contrast ratio line in color picker", true);
-        Runtime.experiments.register("darkTheme", "Dark theme", true);
         Runtime.experiments.register("deviceMode", "Device mode", true);
         Runtime.experiments.register("emptySourceMapAutoStepping", "Empty sourcemap auto-stepping");
         Runtime.experiments.register("fileSystemInspection", "FileSystem inspection");
@@ -168,9 +167,6 @@ WebInspector.Main.prototype = {
 
         WebInspector.initializeUIUtils(window);
         WebInspector.installComponentRootStyles(/** @type {!Element} */ (document.body));
-        if (Runtime.experiments.isEnabled("darkTheme")) {
-            document.body.classList.add("dark-theme");
-        }
 
         this._addMainEventListeners(document);