Add deferred texture upload API.

src/core/SkPixmap.cpp

Index: src/core/SkPixmap.cpp
diff --git a/src/core/SkPixmap.cpp b/src/core/SkPixmap.cpp
index 57bb194258d5f2bdc7b6eb1953c2108d565eaf2b..d7c4cffb7ecea0d6d25c3cec50b804f83e62c7f9 100644
--- a/src/core/SkPixmap.cpp
+++ b/src/core/SkPixmap.cpp
@@ -287,11 +287,19 @@ SkAutoPixmapStorage::~SkAutoPixmapStorage() {
     this->freeStorage();
 }
 
+size_t SkAutoPixmapStorage::AllocSize(const SkImageInfo& info, size_t* rowBytes) {
+    size_t rb = info.minRowBytes();
+    if (rowBytes) {
+        *rowBytes = rb;
+    }
+    return info.getSafeSize(rb);
+}
+
 bool SkAutoPixmapStorage::tryAlloc(const SkImageInfo& info) {
     this->freeStorage();
-    
-    size_t rb = info.minRowBytes();
-    size_t size = info.getSafeSize(rb);
+
+    size_t rb;
+    size_t size = AllocSize(info, &rb);
     if (0 == size) {
         return false;
     }