Switch to one single bitmap text blob cache allocation

src/core/SkDescriptor.h

Index: src/core/SkDescriptor.h
diff --git a/src/core/SkDescriptor.h b/src/core/SkDescriptor.h
index 22ec29316fd30094ed6ad36cff8150acde8808cd..0693ccfe60d82226b95eb5f73e69fc16b46cd9de 100644
--- a/src/core/SkDescriptor.h
+++ b/src/core/SkDescriptor.h
@@ -134,7 +134,13 @@ private:
 
 class SkAutoDescriptor : SkNoncopyable {
 public:
-    SkAutoDescriptor(size_t size) {
+    SkAutoDescriptor() : fDesc(NULL) {}
+    SkAutoDescriptor(size_t size) : fDesc(NULL) { this->reset(size); }
+
+    ~SkAutoDescriptor() { this->free(); }
+
+    void reset(size_t size) {
+        this->free();
         if (size <= sizeof(fStorage)) {
             fDesc = (SkDescriptor*)(void*)fStorage;
         } else {
@@ -142,14 +148,14 @@ public:
         }
     }
 
-    ~SkAutoDescriptor() {
+    SkDescriptor* getDesc() const { SkASSERT(fDesc); return fDesc; }
+private:
+    void free() {
         if (fDesc != (SkDescriptor*)(void*)fStorage) {
             SkDescriptor::Free(fDesc);
         }
     }
 
-    SkDescriptor* getDesc() const { return fDesc; }
-private:
     enum {
         kStorageSize =  sizeof(SkDescriptor)
                         + sizeof(SkDescriptor::Entry) + sizeof(SkScalerContext::Rec)    // for rec