[DevTools] Make unused ScreencastFrameMetadata properties optional

BUG=397107

Review URL: https://codereview.chromium.org/722173002

git-svn-id: svn://svn.chromium.org/blink/trunk@185445 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/devtools/protocol.json

@@ -209,13 +209,13 @@
                 "type": "object",
                 "description": "Screencast frame metadata",
                 "properties": [
-                    { "name": "deviceScaleFactor", "type": "number", "hidden": true, "description": "Device scale factor." },
-                    { "name": "viewport", "$ref": "DOM.Rect", "hidden": true, "description": "Viewport in CSS pixels." },
-                    { "name": "offsetTop", "type": "number", "hidden": true, "optional": true, "description": "Top offset in DIP." },
+                    { "name": "deviceScaleFactor", "type": "number", "hidden": true, "optional": true, "description": "Device scale factor." },
+                    { "name": "viewport", "$ref": "DOM.Rect", "hidden": true, "optional": true, "description": "Viewport in CSS pixels." },
+                    { "name": "offsetTop", "type": "number", "hidden": true, "description": "Top offset in DIP." },
                     { "name": "offsetBottom", "type": "number", "hidden": true, "optional": true, "description": "Bottom offset in DIP." },
                     { "name": "pageScaleFactor", "type": "number", "hidden": true, "description": "Page scale factor." },
-                    { "name": "pageScaleFactorMin", "type": "number", "hidden": true, "description": "Page scale factor min." },
-                    { "name": "pageScaleFactorMax", "type": "number", "hidden": true, "description": "Page scale factor max." },
+                    { "name": "pageScaleFactorMin", "type": "number", "hidden": true, "optional": true, "description": "Page scale factor min." },
+                    { "name": "pageScaleFactorMax", "type": "number", "hidden": true, "optional": true, "description": "Page scale factor max." },
                     { "name": "deviceWidth", "type": "number", "hidden": true, "description": "Device screen width in DIP." },
                     { "name": "deviceHeight", "type": "number", "hidden": true, "description": "Device screen height in DIP." },
                     { "name": "scrollOffsetX", "type": "number", "hidden": true, "description": "Position of horizontal scroll in CSS pixels." },