[SVG2] Add support for the 'turn' unit in <angle>.

Source/core/svg/SVGAngleTearOff.cpp

Index: Source/core/svg/SVGAngleTearOff.cpp
diff --git a/Source/core/svg/SVGAngleTearOff.cpp b/Source/core/svg/SVGAngleTearOff.cpp
index 8a5f832ace8e6ee456c1aa82d5aebe6f3d21c665..33145fce03db9f490deee4cff18a76626afd1fed 100644
--- a/Source/core/svg/SVGAngleTearOff.cpp
+++ b/Source/core/svg/SVGAngleTearOff.cpp
@@ -32,6 +32,7 @@
 #include "core/svg/SVGAngleTearOff.h"
 
 #include "bindings/v8/ExceptionState.h"
+#include "bindings/v8/ExceptionStatePlaceholder.h"
 #include "core/dom/ExceptionCode.h"
 
 namespace WebCore {
@@ -108,7 +109,16 @@ void SVGAngleTearOff::setValueAsString(const String& value, ExceptionState& exce
         return;
     }
 
+    String oldValue = target()->valueAsString();
+
     target()->setValueAsString(value, exceptionState);
+
+    if (!exceptionState.hadException() && !hasExposedAngleUnit()) {
+        target()->setValueAsString(oldValue, ASSERT_NO_EXCEPTION); // rollback to old value
+        exceptionState.throwDOMException(SyntaxError, "The value provided ('" + value + "') is invalid.");
+        return;
+    }
+
     commitChange();
 }