Fix bmp RLE "bug" and add invalid image test to CodexTest

src/codec/SkBmpCodec.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBmpCodec.h"
 #include "SkBmpMaskCodec.h"
 #include "SkBmpRLECodec.h"
@@ skipping 460 matching lines @@
         // Return the codec
         switch (inputFormat) {
             case kStandard_BmpInputFormat:
                 *codecOut = SkNEW_ARGS(SkBmpStandardCodec, (imageInfo, stream,
                         bitsPerPixel, numColors, bytesPerColor,
                         offset - bytesRead, rowOrder, inIco));
                 return true;
             case kBitMask_BmpInputFormat:
                 // Bmp-in-Ico must be standard mode
                 if (inIco) {
+                    SkCodecPrintf("Error: Icos may not use bit mask format.\n");
                     return false;
                 }
                 // Skip to the start of the pixel array.
                 // We can do this here because there is no color table to read
                 // in bit mask mode.
                 if (stream->skip(offset - bytesRead) != offset - bytesRead) {
                     SkCodecPrintf("Error: unable to skip to image data.\n");
                     return false;
                 }
 
                 *codecOut = SkNEW_ARGS(SkBmpMaskCodec, (imageInfo, stream,
                         bitsPerPixel, masks.detach(), rowOrder));
                 return true;
             case kRLE_BmpInputFormat:
                 // Bmp-in-Ico must be standard mode
-                if (inIco) {
-                    return false;
-                }
+                // When inIco is true, this line cannot be reached, since we
+                // require that RLE Bmps have a valid number of totalBytes, and
+                // Icos skip the header that contains totalBytes.
+                SkASSERT(!inIco);
                 *codecOut = SkNEW_ARGS(SkBmpRLECodec, (
                         imageInfo, stream, bitsPerPixel, numColors,
                         bytesPerColor, offset - bytesRead, rowOrder, RLEBytes));
                 return true;
             default:
                 SkASSERT(false);
                 return false;
         }
     }
 
@@ skipping 48 matching lines @@
  */
 void* SkBmpCodec::getDstStartRow(void* dst, size_t dstRowBytes, int32_t y) const {
     return (kTopDown_RowOrder == fRowOrder) ? SkTAddOffset<void*>(dst, y * dstRowBytes) : dst;
 }
 
 /*
  * Compute the number of colors in the color table
  */
 uint32_t SkBmpCodec::computeNumColors(uint32_t numColors) {
     // Zero is a default for maxColors
-    // Also set fNumColors to maxColors when it is too large
+    // Also set numColors to maxColors when it is too large
     uint32_t maxColors = 1 << fBitsPerPixel;
     if (numColors == 0 || numColors >= maxColors) {
         return maxColors;
     }
     return numColors;
 }