diff -r 000000000000 -r 6474c204b198 layout/style/nsMediaFeatures.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/style/nsMediaFeatures.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,75 @@
+/* vim: set shiftwidth=4 tabstop=8 autoindent cindent expandtab: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* the features that media queries can test */
+
+#ifndef nsMediaFeatures_h_
+#define nsMediaFeatures_h_
+
+#include "nsError.h"
+#include "nsCSSProps.h"
+
+class nsIAtom;
+class nsPresContext;
+class nsCSSValue;
+
+struct nsMediaFeature;
+typedef nsresult
+(* nsMediaFeatureValueGetter)(nsPresContext* aPresContext,
+                              const nsMediaFeature* aFeature,
+                              nsCSSValue& aResult);
+
+struct nsMediaFeature {
+    nsIAtom **mName; // extra indirection to point to nsGkAtoms members
+
+    enum RangeType { eMinMaxAllowed, eMinMaxNotAllowed };
+    RangeType mRangeType;
+
+    enum ValueType {
+        // All value types allow eCSSUnit_Null to indicate that no value
+        // was given (in addition to the types listed below).
+        eLength,     // values are such that nsCSSValue::IsLengthUnit() is true
+        eInteger,    // values are eCSSUnit_Integer
+        eFloat,      // values are eCSSUnit_Number
+        eBoolInteger,// values are eCSSUnit_Integer (0, -0, or 1 only)
+        eIntRatio,   // values are eCSSUnit_Array of two eCSSUnit_Integer
+        eResolution, // values are in eCSSUnit_Inch (for dpi),
+                     //   eCSSUnit_Pixel (for dppx), or
+                     //   eCSSUnit_Centimeter (for dpcm)
+        eEnumerated, // values are eCSSUnit_Enumerated (uses keyword table)
+        eIdent       // values are eCSSUnit_Ident
+        // Note that a number of pieces of code (both for parsing and
+        // for matching of valueless expressions) assume that all numeric
+        // value types cannot be negative.  The parsing code also does
+        // not allow zeros in eIntRatio types.
+    };
+    ValueType mValueType;
+
+    union {
+      // In static arrays, it's the first member that's initialized.  We
+      // need that to be void* so we can initialize both other types.
+      // This member should never be accessed by name.
+      const void* mInitializer_;
+      // If mValueType == eEnumerated:  const int32_t*: keyword table in
+      //   the same format as the keyword tables in nsCSSProps.
+      const nsCSSProps::KTableValue* mKeywordTable;
+      // If mGetter == GetSystemMetric (which implies mValueType ==
+      //   eBoolInteger): nsIAtom * const *, for the system metric.
+      nsIAtom * const * mMetric;
+    } mData;
+
+    // A function that returns the current value for this feature for a
+    // given presentation.  If it returns eCSSUnit_Null, the feature is
+    // not present.
+    nsMediaFeatureValueGetter mGetter;
+};
+
+class nsMediaFeatures {
+public:
+    // Terminated with an entry whose mName is null.
+    static const nsMediaFeature features[];
+};
+
+#endif /* !defined(nsMediaFeatures_h_) */