Consolidate read-only exception throwing for SVG*TearOffs

third_party/WebKit/Source/core/svg/SVGMatrixTearOff.cpp

Index: third_party/WebKit/Source/core/svg/SVGMatrixTearOff.cpp
diff --git a/third_party/WebKit/Source/core/svg/SVGMatrixTearOff.cpp b/third_party/WebKit/Source/core/svg/SVGMatrixTearOff.cpp
index bc157eff7b77bd4ec50ab45320c97e4d6fe023d0..c2a28840b22a20fb54360be9642ed2e9f5af8aab 100644
--- a/third_party/WebKit/Source/core/svg/SVGMatrixTearOff.cpp
+++ b/third_party/WebKit/Source/core/svg/SVGMatrixTearOff.cpp
@@ -77,7 +77,7 @@ void SVGMatrixTearOff::commitChange()
     void SVGMatrixTearOff::set##ATTRIBUTE(double f, ExceptionState& exceptionState) \
     { \
         if (m_contextTransform && m_contextTransform->isImmutable()) { \
-            exceptionState.throwDOMException(NoModificationAllowedError, "The attribute is read-only."); \
+            SVGPropertyTearOffBase::throwReadOnly(exceptionState); \
             return; \
         } \
         mutableValue()->set##ATTRIBUTE(f); \
@@ -158,18 +158,19 @@ SVGMatrixTearOff* SVGMatrixTearOff::multiply(SVGMatrixTearOff* other)
 
 SVGMatrixTearOff* SVGMatrixTearOff::inverse(ExceptionState& exceptionState)
 {
-    AffineTransform transform = value().inverse();
-    if (!value().isInvertible())
+    if (!value().isInvertible()) {
         exceptionState.throwDOMException(InvalidStateError, "The matrix is not invertible.");
-
-    return create(transform);
+        return nullptr;
+    }
+    return create(value().inverse());
 }
 
 SVGMatrixTearOff* SVGMatrixTearOff::rotateFromVector(double x, double y, ExceptionState& exceptionState)
 {
-    if (!x || !y)
+    if (!x || !y) {
         exceptionState.throwDOMException(InvalidAccessError, "Arguments cannot be zero.");
-
+        return nullptr;
+    }
     AffineTransform copy = value();
     copy.rotateFromVector(x, y);
     return create(copy);