Expose CSSViewportRule only if runtime flag is enabled.

Bug: 766652
Change-Id: I7e76640a397eafeba28f178fb568b3af7cdccf49
Reviewed-on: https://chromium-review.googlesource.com/674924
Reviewed-by: Rick Byers <rbyers@chromium.org>
Commit-Queue: Rune Lillesveen <rune@opera.com>
Cr-Commit-Position: refs/heads/master@{#503370}
diff --git a/third_party/WebKit/LayoutTests/platform/mac/virtual/stable/webexposed/global-interface-listing-expected.txt b/third_party/WebKit/LayoutTests/platform/mac/virtual/stable/webexposed/global-interface-listing-expected.txt
index 9e21254..d7f91ca 100644
--- a/third_party/WebKit/LayoutTests/platform/mac/virtual/stable/webexposed/global-interface-listing-expected.txt
+++ b/third_party/WebKit/LayoutTests/platform/mac/virtual/stable/webexposed/global-interface-listing-expected.txt
@@ -456,10 +456,6 @@
 interface CSSSupportsRule : CSSConditionRule
     attribute @@toStringTag
     method constructor
-interface CSSViewportRule : CSSRule
-    attribute @@toStringTag
-    getter style
-    method constructor
 interface Cache
     attribute @@toStringTag
     method add
diff --git a/third_party/WebKit/LayoutTests/platform/win/virtual/stable/webexposed/global-interface-listing-expected.txt b/third_party/WebKit/LayoutTests/platform/win/virtual/stable/webexposed/global-interface-listing-expected.txt
index 46734b3..d58c0a8 100644
--- a/third_party/WebKit/LayoutTests/platform/win/virtual/stable/webexposed/global-interface-listing-expected.txt
+++ b/third_party/WebKit/LayoutTests/platform/win/virtual/stable/webexposed/global-interface-listing-expected.txt
@@ -385,10 +385,6 @@
 interface CSSSupportsRule : CSSConditionRule
     attribute @@toStringTag
     method constructor
-interface CSSViewportRule : CSSRule
-    attribute @@toStringTag
-    getter style
-    method constructor
 interface Cache
     attribute @@toStringTag
     method add
diff --git a/third_party/WebKit/Source/core/css/CSSViewportRule.idl b/third_party/WebKit/Source/core/css/CSSViewportRule.idl
index cec67e6..4c1894b 100644
--- a/third_party/WebKit/Source/core/css/CSSViewportRule.idl
+++ b/third_party/WebKit/Source/core/css/CSSViewportRule.idl
@@ -29,6 +29,8 @@
 
 // https://drafts.csswg.org/css-device-adapt/#css-viewport-rule-interface
 
-interface CSSViewportRule : CSSRule {
+[
+    RuntimeEnabled=CSSViewport
+] interface CSSViewportRule : CSSRule {
     readonly attribute CSSStyleDeclaration style;
 };