Attempt to improve lifetime management of SkGlyphCache in Ganesh atlas text code.

src/core/SkDescriptor.h

Index: src/core/SkDescriptor.h
diff --git a/src/core/SkDescriptor.h b/src/core/SkDescriptor.h
index 736021953b8fc34f22d43e3cd6e9e619ba1c8f0d..71f71336fd6780979dae600864437a9122aacfb3 100644
--- a/src/core/SkDescriptor.h
+++ b/src/core/SkDescriptor.h
@@ -102,6 +102,7 @@ public:
         } while (aa < stop);
         return true;
     }
+    bool operator!=(const SkDescriptor& other) const { return !(*this == other); }
 
     uint32_t getChecksum() const { return fChecksum; }