change API contract: disallow zero-sized images or surfaces

src/image/SkSurface_Raster.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkSurface_Base.h"
 #include "SkImagePriv.h"
 #include "SkCanvas.h"
@@ skipping 21 matching lines @@
 private:
     SkBitmap    fBitmap;
     bool        fWeOwnThePixels;
 
     typedef SkSurface_Base INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
 bool SkSurface_Raster::Valid(const SkImageInfo& info, size_t rowBytes) {
+    if (info.isEmpty()) {
+        return false;
+    }
+
     static const size_t kMaxTotalSize = SK_MaxS32;
 
     int shift = 0;
     switch (info.colorType()) {
         case kAlpha_8_SkColorType:
             shift = 0;
             break;
         case kRGB_565_SkColorType:
             shift = 1;
             break;
@@ skipping 113 matching lines @@
     if (!SkSurface_Raster::Valid(info)) {
         return NULL;
     }
 
     SkAutoTUnref<SkPixelRef> pr(SkMallocPixelRef::NewAllocate(info, 0, NULL));
     if (NULL == pr.get()) {
         return NULL;
     }
     return SkNEW_ARGS(SkSurface_Raster, (pr, props));
 }