[CSSMQ] Use initial values as base for relative units.

Source/core/css/MediaQueryEvaluator.cpp

Index: Source/core/css/MediaQueryEvaluator.cpp
diff --git a/Source/core/css/MediaQueryEvaluator.cpp b/Source/core/css/MediaQueryEvaluator.cpp
index 900a6271c08e1f5992d9d651f9106da4b5b3b172..413c80ea910c3007cd921b8f22239eb7c74a7f44 100644
--- a/Source/core/css/MediaQueryEvaluator.cpp
+++ b/Source/core/css/MediaQueryEvaluator.cpp
@@ -337,7 +337,7 @@ static bool gridMediaFeatureEval(CSSValue* value, RenderStyle*, Frame*, MediaFea
     return false;
 }
 
-static bool computeLength(CSSValue* value, bool strict, RenderStyle* style, RenderStyle* rootStyle, int& result)
+static bool computeLength(CSSValue* value, bool strict, RenderStyle* initialStyle, int& result)
 {
     if (!value->isPrimitiveValue())
         return false;
@@ -350,7 +350,9 @@ static bool computeLength(CSSValue* value, bool strict, RenderStyle* style, Rend
     }
 
     if (primitiveValue->isLength()) {
-        result = primitiveValue->computeLength<int>(style, rootStyle, 1.0 /* multiplier */, true /* computingFontSize */);
+        // Relative (like EM) and root relative (like REM) units are always resolved against the initial values
+        // for media queries, hence the two initialStyle parameters.
+        result = primitiveValue->computeLength<int>(initialStyle, initialStyle, 1.0 /* multiplier */, true /* computingFontSize */);
         return true;
     }
 
@@ -361,11 +363,10 @@ static bool deviceHeightMediaFeatureEval(CSSValue* value, RenderStyle* style, Fr
 {
     if (value) {
         FloatRect sg = screenRect(frame->page()->mainFrame()->view());
-        RenderStyle* rootStyle = frame->document()->documentElement()->renderStyle();
         int length;
         long height = sg.height();
         InspectorInstrumentation::applyScreenHeightOverride(frame, &height);
-        return computeLength(value, !frame->document()->inQuirksMode(), style, rootStyle, length) && compareValue(static_cast<int>(height), length, op);
+        return computeLength(value, !frame->document()->inQuirksMode(), style, length) && compareValue(static_cast<int>(height), length, op);
     }
     // ({,min-,max-}device-height)
     // assume if we have a device, assume non-zero
@@ -376,11 +377,10 @@ static bool deviceWidthMediaFeatureEval(CSSValue* value, RenderStyle* style, Fra
 {
     if (value) {
         FloatRect sg = screenRect(frame->page()->mainFrame()->view());
-        RenderStyle* rootStyle = frame->document()->documentElement()->renderStyle();
         int length;
         long width = sg.width();
         InspectorInstrumentation::applyScreenWidthOverride(frame, &width);
-        return computeLength(value, !frame->document()->inQuirksMode(), style, rootStyle, length) && compareValue(static_cast<int>(width), length, op);
+        return computeLength(value, !frame->document()->inQuirksMode(), style, length) && compareValue(static_cast<int>(width), length, op);
     }
     // ({,min-,max-}device-width)
     // assume if we have a device, assume non-zero
@@ -395,9 +395,8 @@ static bool heightMediaFeatureEval(CSSValue* value, RenderStyle* style, Frame* f
     if (value) {
         if (RenderView* renderView = frame->document()->renderView())
             height = adjustForAbsoluteZoom(height, renderView);
-        RenderStyle* rootStyle = frame->document()->documentElement()->renderStyle();
         int length;
-        return computeLength(value, !frame->document()->inQuirksMode(), style, rootStyle, length) && compareValue(height, length, op);
+        return computeLength(value, !frame->document()->inQuirksMode(), style, length) && compareValue(height, length, op);
     }
 
     return height;
@@ -411,9 +410,8 @@ static bool widthMediaFeatureEval(CSSValue* value, RenderStyle* style, Frame* fr
     if (value) {
         if (RenderView* renderView = frame->document()->renderView())
             width = adjustForAbsoluteZoom(width, renderView);
-        RenderStyle* rootStyle = frame->document()->documentElement()->renderStyle();
         int length;
-        return computeLength(value, !frame->document()->inQuirksMode(), style, rootStyle, length) && compareValue(width, length, op);
+        return computeLength(value, !frame->document()->inQuirksMode(), style, length) && compareValue(width, length, op);
     }
 
     return width;