Revert "Revert of Use the GrCacheable ID to eliminate the need for notifications to GrGpuGL when textures and RTs are… (https://codereview.chromium.org/376703009/)"

This reverts commit 249171e7d29b5559f3eefe9dbd437030bfad3fda.

Uses 32 bit id instead of 64. Renamed instanceID to uniqueID to match existing code.

R=robertphillips@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/414493002
diff --git a/src/gpu/GrBitmapTextContext.h b/src/gpu/GrBitmapTextContext.h
index b9d5ce7..6d4ea6d 100644
--- a/src/gpu/GrBitmapTextContext.h
+++ b/src/gpu/GrBitmapTextContext.h
@@ -48,7 +48,8 @@
     int32_t                     fMaxVertices;
     GrTexture*                  fCurrTexture;
     SkAutoTUnref<GrEffect>      fCachedEffect;
-    uint32_t                    fEffectTextureGenID;
+    // Used to check whether fCachedEffect is still valid.
+    uint32_t                    fEffectTextureUniqueID;
     int                         fCurrVertex;
     SkRect                      fVertexBounds;
 };