fix some small bugs with GrAtlasTextContext

src/gpu/GrAtlasTextContext.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrAtlasTextContext_DEFINED
 #define GrAtlasTextContext_DEFINED
 
@@ skipping 230 matching lines @@
 
         // We can reuse distance field text, but only if the new viewmatrix would not result in
         // a mip change.  Because there can be multiple runs in a blob, we track the overall
         // maximum minimum scale, and minimum maximum scale, we can support before we need to regen
         SkScalar fMaxMinScale;
         SkScalar fMinMaxScale;
         int fRunCount;
         uint8_t fTextType;
 
         BitmapTextBlob()
-            : fMaxMinScale(SK_ScalarMax)
+            : fMaxMinScale(-SK_ScalarMax)
             , fMinMaxScale(SK_ScalarMax)
             , fTextType(0) {}
 
         static const Key& GetKey(const BitmapTextBlob& blob) {
             return blob.fKey;
         }
 
         static uint32_t Hash(const Key& key) {
             return SkChecksum::Murmur3(&key, sizeof(Key));
         }
@@ skipping 132 matching lines @@
     bool fEnableDFRendering;
     SkAutoTUnref<DistanceAdjustTable> fDistanceAdjustTable;
 
     friend class GrTextBlobCache;
     friend class BitmapTextBatch;
 
     typedef GrTextContext INHERITED;
 };
 
 #endif