Call reset() in text context rather than set to SkMatrix::I(). Perf improvement in bench.



git-svn-id: http://skia.googlecode.com/svn/trunk@3415 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/GrDefaultTextContext.cpp b/src/gpu/GrDefaultTextContext.cpp
index bde06c6..93b7e2c 100644
--- a/src/gpu/GrDefaultTextContext.cpp
+++ b/src/gpu/GrDefaultTextContext.cpp
@@ -81,7 +81,7 @@
     if (NULL != extMatrix) {
         fExtMatrix = *extMatrix;
     } else {
-        fExtMatrix = GrMatrix::I();
+        fExtMatrix.reset();
     }
     if (context->getClip().hasConservativeBounds()) {
         if (!fExtMatrix.isIdentity()) {