Rename GrBitmapTextContextB to GrAtlasTextContext

BUG=skia:

Review URL: https://codereview.chromium.org/1050173002
diff --git a/src/gpu/GrStencilAndCoverTextContext.cpp b/src/gpu/GrStencilAndCoverTextContext.cpp
index 1df8f16..1456aa2 100644
--- a/src/gpu/GrStencilAndCoverTextContext.cpp
+++ b/src/gpu/GrStencilAndCoverTextContext.cpp
@@ -36,7 +36,7 @@
     GrStencilAndCoverTextContext* textContext = SkNEW_ARGS(GrStencilAndCoverTextContext,
                                                            (context, gpuDevice, props));
 #ifdef USE_BITMAP_TEXTBLOBS
-    textContext->fFallbackTextContext = GrBitmapTextContextB::Create(context, gpuDevice, props);
+    textContext->fFallbackTextContext = GrAtlasTextContext::Create(context, gpuDevice, props);
 #else
     textContext->fFallbackTextContext = GrBitmapTextContext::Create(context, gpuDevice, props);
 #endif