Add a method to read a stream without advancing it.

src/core/SkStream.cpp

Index: src/core/SkStream.cpp
diff --git a/src/core/SkStream.cpp b/src/core/SkStream.cpp
index 426f5569e887fe83e4aee8b38c412587abfa1fe2..2a07a114397c4b342a04abba3f3258af33b32682 100644
--- a/src/core/SkStream.cpp
+++ b/src/core/SkStream.cpp
@@ -367,6 +367,23 @@ size_t SkMemoryStream::read(void* buffer, size_t size) {
     return size;
 }
 
+bool SkMemoryStream::peek(void* buffer, size_t size) const {
+    SkASSERT(buffer != NULL);
+    const size_t position = fOffset;
+    if (size > fData->size() - position) {
+        // The stream is not large enough to satisfy this request.
+        return false;
+    }
+    SkMemoryStream* nonConstThis = const_cast<SkMemoryStream*>(this);
+#ifdef SK_DEBUG

[bungeman-skia, 2015/04/02 18:24:09]

Should this be SkDEBUGCODE(...) instead? Then it would fit on the one line, like

SkDEBUGCODE(const size_t bytesRead =) nonConstThis->read(buffer, size); 

[scroggo, 2015/04/02 19:49:43]

Yes. Much better.

+    const size_t bytesRead =
+#endif
+    nonConstThis->read(buffer, size);
+    SkASSERT(bytesRead == size);
+    nonConstThis->fOffset = position;
+    return true;
+}
+
 bool SkMemoryStream::isAtEnd() const {
     return fOffset == fData->size();
 }