Refactor position computation to enable device space "nudge"

src/gpu/GrGeometryProcessor.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGeometryProcessor_DEFINED
 #define GrGeometryProcessor_DEFINED
 
@@ skipping 202 matching lines @@
         return true;
     }
 
     Attribute fAttribs[kMaxVertexAttribs];
     int fNumAttribs;
     size_t fVertexStride;
 
 private:
     virtual bool hasExplicitLocalCoords() const = 0;
 
-    SkMatrix fViewMatrix;
+    const SkMatrix fViewMatrix;
     SkMatrix fLocalMatrix;
 
     typedef GrProcessor INHERITED;
 };
 
 /**
  * A GrGeometryProcessor is a flexible method for rendering a primitive.  The GrGeometryProcessor
  * has complete control over vertex attributes and uniforms(aside from the render target) but it
  * must obey the same contract as any GrPrimitiveProcessor, specifically it must emit a color and
  * coverage into the fragment shader.  Where this color and coverage come from is completely the
@@ skipping 173 matching lines @@
 
 private:
     bool hasExplicitLocalCoords() const SK_OVERRIDE { return false; }
 
     GrColor fColor;
 
     typedef GrPrimitiveProcessor INHERITED;
 };
 
 #endif