Moved remaining legacy viewport tests to unit tests.

Source/core/css/ViewportStyle.h

Index: Source/core/css/ViewportStyle.h
diff --git a/Source/core/css/ViewportStyle.h b/Source/core/css/ViewportStyle.h
index 903ad0fe81c180def8cb398c337f5fc8e1224d4e..44d42d5dc81a6a92af1362d79d52c3e930dbb674 100644
--- a/Source/core/css/ViewportStyle.h
+++ b/Source/core/css/ViewportStyle.h
@@ -28,11 +28,36 @@
 
 #include "wtf/text/WTFString.h"
 
+namespace blink {
+namespace FrameTestHelpers {
+class ReplaceViewportUAStylesheet;
+}
+}
+
 namespace WebCore {
 
 class ViewportStyle {
 public:
-    static String viewportStyleSheet();
+    static String viewportStyleSheet()
+    {
+        if (!styleOverrideString().isEmpty())
+            return styleOverrideString();
+
+        return platformStyleSheet();
+    }
+
+private:
+    // Implemented in platform-dependent files to return the viewport style to
+    // use on specific platforms.
+    static String platformStyleSheet();
+
+    // Allows tests to override the platform specific stylesheet
+    friend class blink::FrameTestHelpers::ReplaceViewportUAStylesheet;
+    static String& styleOverrideString()
+    {
+        static String &styleString = *new String();
+        return styleString;
+    }
 };
 
 } // namespace WebCore