Add 'skiapict' magic bytes to SkPicture format.

src/core/SkPicture.cpp

Index: src/core/SkPicture.cpp
diff --git a/src/core/SkPicture.cpp b/src/core/SkPicture.cpp
index 1df56a52d784bbd85ca1dc58d2651b021bb7d78e..d4db196cb66601f96e2376909fae52068992b7bc 100644
--- a/src/core/SkPicture.cpp
+++ b/src/core/SkPicture.cpp
@@ -266,11 +266,20 @@ void SkPicture::draw(SkCanvas* surface, SkDrawPictureCallback* callback) {
 
 #include "SkStream.h"
 
+static const char kMagic[] = { 's', 'k', 'i', 'a', 'p', 'i', 'c', 't' };
+
 bool SkPicture::StreamIsSKP(SkStream* stream, SkPictInfo* pInfo) {
     if (NULL == stream) {
         return false;
     }
 
+    // Check magic bytes.
+    uint8_t magic[SK_ARRAY_COUNT(kMagic)];

[reed1, 2013/10/16 15:34:41]

could be sizeof or SK_ARRAY_COUNT. I find the former slightly clearer, but no
big pref.

+    stream->read(magic, SK_ARRAY_COUNT(kMagic));
+    if (0 != memcmp(magic, kMagic, SK_ARRAY_COUNT(kMagic))) {
+        return false;
+    }
+
     SkPictInfo info;
     if (!stream->read(&info, sizeof(SkPictInfo))) {
         return false;
@@ -341,6 +350,10 @@ void SkPicture::serialize(SkWStream* stream, EncodeBitmap encoder) const {
         info.fFlags |= SkPictInfo::kPtrIs64Bit_Flag;
     }
 
+    // Write 8 magic bytes to ID this file format.
+    SkASSERT(SK_ARRAY_COUNT(kMagic) == 8);
+    stream->write(kMagic, SK_ARRAY_COUNT(kMagic));
+
     stream->write(&info, sizeof(info));
     if (playback) {
         stream->writeBool(true);