Add default ctor to SkMask

src/core/SkBitmap.cpp

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkAtomics.h"
 #include "SkBitmap.h"
 #include "SkColorPriv.h"
@@ skipping 1015 matching lines @@
 
     srcM.fBounds.set(0, 0, this->width(), this->height());
     srcM.fRowBytes = SkAlign4(this->width());
     srcM.fFormat = SkMask::kA8_Format;
 
     SkMaskFilter* filter = paint ? paint->getMaskFilter() : nullptr;
 
     // compute our (larger?) dst bounds if we have a filter
     if (filter) {
         identity.reset();
-        srcM.fImage = nullptr;
         if (!filter->filterMask(&dstM, srcM, identity, nullptr)) {
             goto NO_FILTER_CASE;
         }
         dstM.fRowBytes = SkAlign4(dstM.fBounds.width());
     } else {
     NO_FILTER_CASE:
         tmpBitmap.setInfo(SkImageInfo::MakeA8(this->width(), this->height()), srcM.fRowBytes);
         if (!tmpBitmap.tryAllocPixels(allocator, nullptr)) {
             // Allocation of pixels for alpha bitmap failed.
             SkDebugf("extractAlpha failed to allocate (%d,%d) alpha bitmap\n",
@@ skipping 291 matching lines @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #ifdef SK_DEBUG
 void SkImageInfo::validate() const {
     SkASSERT(fWidth >= 0);
     SkASSERT(fHeight >= 0);
     SkASSERT(SkColorTypeIsValid(fColorType));
     SkASSERT(SkAlphaTypeIsValid(fAlphaType));
 }
 #endif