[devtools] Add a command to emulate the default background color.

third_party/WebKit/Source/core/inspector/browser_protocol.json

Index: third_party/WebKit/Source/core/inspector/browser_protocol.json
diff --git a/third_party/WebKit/Source/core/inspector/browser_protocol.json b/third_party/WebKit/Source/core/inspector/browser_protocol.json
index f06ae7ec5705025a8be7e37a301c4246db2f048d..731b2dcb5f7822fd866edea7c86642f3390e56d0 100644
--- a/third_party/WebKit/Source/core/inspector/browser_protocol.json
+++ b/third_party/WebKit/Source/core/inspector/browser_protocol.json
@@ -693,6 +693,7 @@
     {
         "domain": "Emulation",
         "description": "This domain emulates different environments for the page.",
+        "dependencies": ["DOM"],
         "types": [
             {
                 "id": "ScreenOrientation",
@@ -838,6 +839,14 @@
                     { "name": "budget", "type": "integer", "optional": true, "description": "If set, after this many virtual milliseconds have elapsed virtual time will be paused and a virtualTimeBudgetExpired event is sent." }
                 ],
                 "experimental": true
+            },
+            {
+                "name": "setDefaultBackgroundColorOverride",
+                "description": "Sets or clears an override of the default background color of the frame. This override is used if the content does not specify one.",
+                "parameters": [
+                    { "name": "color", "$ref": "DOM.RGBA", "optional": true, "description": "RGBA of the default background color. If not specified, any existing override will be cleared." }
+                ],
+                "experimental": true
             }
         ],
         "events": [