[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 ee61904d0623f42ee37aed7cbec0ef15cc83a6b2..fea4ae82c345ea6cafa21cde4b976a86a5a03881 100644
--- a/third_party/WebKit/Source/core/inspector/browser_protocol.json
+++ b/third_party/WebKit/Source/core/inspector/browser_protocol.json
@@ -689,6 +689,7 @@
     {
         "domain": "Emulation",
         "description": "This domain emulates different environments for the page.",
+        "dependencies": ["DOM"],
         "types": [
             {
                 "id": "ScreenOrientation",
@@ -834,6 +835,14 @@
                     { "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": "setDefaultBackgroundColor",
+                "description": "Sets the default background color of the frame that is used if the content does not specify one.",
+                "parameters": [
+                    { "name": "color", "$ref": "DOM.RGBA", "description": "RGBA of the default background color." }
+                ],
+                "experimental": true
             }
         ],
         "events": [