Careful not to read/write past (conservative) allocation size of SkBitmap

related to https://skia-review.googlesource.com/c/skia/+/50980

Bug: 
Change-Id: I670b4f239cdbedd64892d6de5dd24232ba1ae8ac
Reviewed-on: https://chromium-review.googlesource.com/685719
Commit-Queue: Mike Reed <reed@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505139}

ui/gfx/codec/png_codec_unittest.cc

@@ -769,7 +769,6 @@ TEST(PNGCodec, EncodeBGRASkBitmapStridePadded) {
   const int kHeight = 20;
   const int kPaddedWidth = 32;
   const int kBytesPerPixel = 4;
-  const int kPaddedSize = kPaddedWidth * kHeight;
   const int kRowBytes = kPaddedWidth * kBytesPerPixel;
 
   SkImageInfo info = SkImageInfo::MakeN32Premul(kWidth, kHeight);
@@ -781,7 +780,9 @@ TEST(PNGCodec, EncodeBGRASkBitmapStridePadded) {
   // We write on the pad area here too.
   // The encoder should ignore the pad area.
   uint32_t* src_data = original_bitmap.getAddr32(0, 0);
-  for (int i = 0; i < kPaddedSize; i++) {
+  const int count =
+      original_bitmap.getSafeSize() / original_bitmap.bytesPerPixel();
+  for (int i = 0; i < count; i++) {
     src_data[i] = SkPreMultiplyARGB(i % 255, i % 250, i % 245, i % 240);
   }
 

ui/gfx/skia_util.cc

@@ -98,12 +98,12 @@ bool BitmapsAreEqual(const SkBitmap& bitmap1, const SkBitmap& bitmap2) {
   size_t size2 = 0;
 
   addr1 = bitmap1.getAddr32(0, 0);
-  size1 = bitmap1.getSize();
+  size1 = bitmap1.getSafeSize();
 
   addr2 = bitmap2.getAddr32(0, 0);
-  size2 = bitmap2.getSize();
+  size2 = bitmap2.getSafeSize();
 
-  return (size1 == size2) && (0 == memcmp(addr1, addr2, bitmap1.getSize()));
+  return (size1 == size2) && (0 == memcmp(addr1, addr2, size1));
 }
 
 void ConvertSkiaToRGBA(const unsigned char* skia,