Add reallyHasAlpha() to SkAndroidCodec

include/codec/SkCodec.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCodec_DEFINED
 #define SkCodec_DEFINED
 
@@ skipping 268 matching lines @@
 
     /**
      *  Some images may initially report that they have alpha due to the format
      *  of the encoded data, but then never use any colors which have alpha
      *  less than 100%. This function can be called *after* decoding to
      *  determine if such an image truly had alpha. Calling it before decoding
      *  is undefined.
      *  FIXME: see skbug.com/3582.
      */
     bool reallyHasAlpha() const {
-        return this->onReallyHasAlpha();
+        return kOpaque_SkAlphaType != this->getInfo().alphaType() && this->onReallyHasAlpha();
     }
 
     /**
      * The remaining functions revolve around decoding scanlines.
      */
 
     /**
      *  Prepare for a scanline decode with the specified options.
      *
      *  After this call, this class will be ready to decode the first scanline.
@@ skipping 179 matching lines @@
     virtual Result onGetPixels(const SkImageInfo& info,
                                void* pixels, size_t rowBytes, const Options&,
                                SkPMColor ctable[], int* ctableCount,
                                int* rowsDecoded) = 0;
 
     virtual bool onGetValidSubset(SkIRect* /* desiredSubset */) const {
         // By default, subsets are not supported.
         return false;
     }
 
-    virtual bool onReallyHasAlpha() const { return false; }
+    virtual bool onReallyHasAlpha() const {
+        // If the image indicates that it does have alpha, by default, we

[scroggo, 2015/12/10 18:45:44]

Maybe add a comment that this is only called if the alpha type is not opaque?
Also, should this comment go outside the method body?

[msarett, 2015/12/10 18:53:30]

Done and yes.

+        // will assume this to be true. Subclasses may override this
+        // function if they intend to verify that the image actually has
+        // alpha.
+        return true;
+    }
 
     /**
      *  If the stream was previously read, attempt to rewind.
      *
      *  If the stream needed to be rewound, call onRewind.
      *  @returns true if the codec is at the right position and can be used.
      *      false if there was a failure to rewind.
      *
      *  This is called by getPixels() and start(). Subclasses may call if they
      *  need to rewind at another time.
@@ skipping 141 matching lines @@
      *  not affect ownership.
      *
      *  Only valid during scanline decoding.
      */
     virtual SkSampler* getSampler(bool /*createIfNecessary*/) { return nullptr; }
 
     friend class SkSampledCodec;
     friend class SkIcoCodec;
 };
 #endif // SkCodec_DEFINED