Rename GrTextureBufferSampler to GrBufferSampler

Just a simple renaming to reinforce the Ganesh notion that a buffer
access is not related to a texture.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4879

Change-Id: I3f12b6eccff744e246618be0a7abf41c4a1228a1
Reviewed-on: https://skia-review.googlesource.com/4879
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
diff --git a/src/gpu/GrProgramDesc.cpp b/src/gpu/GrProgramDesc.cpp
index fa728ed..ea2a528 100644
--- a/src/gpu/GrProgramDesc.cpp
+++ b/src/gpu/GrProgramDesc.cpp
@@ -19,7 +19,7 @@
                             const GrGLSLCaps& caps) {
     enum {
         kFirstSamplerType = kTexture2DSampler_GrSLType,
-        kLastSamplerType = kTextureBufferSampler_GrSLType,
+        kLastSamplerType = kBufferSampler_GrSLType,
         kSamplerTypeKeyBits = 4
     };
     GR_STATIC_ASSERT(kLastSamplerType - kFirstSamplerType < (1 << kSamplerTypeKeyBits));
@@ -51,7 +51,7 @@
     }
     for (; i < numSamplers; ++i) {
         const GrBufferAccess& access = proc.bufferAccess(i - numTextures);
-        k16[i] = sampler_key(kTextureBufferSampler_GrSLType, access.texelConfig(),
+        k16[i] = sampler_key(kBufferSampler_GrSLType, access.texelConfig(),
                              access.visibility(), caps);
     }
     // zero the last 16 bits if the number of samplers is odd.