check for identity in translate

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 6e898fa1bbb73fdae8b73e7b4241979cf6376b3c..e53a104c47fa28406f1d440dbcd670365d877a24 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -1457,14 +1457,16 @@ void SkCanvas::internalDrawDevice(SkBaseDevice* srcDev, int x, int y, const SkPa
 /////////////////////////////////////////////////////////////////////////////
 
 void SkCanvas::translate(SkScalar dx, SkScalar dy) {
-    this->checkForDeferredSave();
-    fDeviceCMDirty = true;
-    fMCRec->fMatrix.preTranslate(dx,dy);
+    if (dx || dy) {
+        this->checkForDeferredSave();
+        fDeviceCMDirty = true;
+        fMCRec->fMatrix.preTranslate(dx,dy);
 
-    // Translate shouldn't affect the is-scale-translateness of the matrix.
-    SkASSERT(fIsScaleTranslate == fMCRec->fMatrix.isScaleTranslate());
+        // Translate shouldn't affect the is-scale-translateness of the matrix.
+        SkASSERT(fIsScaleTranslate == fMCRec->fMatrix.isScaleTranslate());
 
-    this->didTranslate(dx,dy);
+        this->didTranslate(dx,dy);
+    }
 }
 
 void SkCanvas::scale(SkScalar sx, SkScalar sy) {