Fix unit test crash caused by OSMesa not supporting rendering to GL_ALPHA8

src/gpu/gl/GrGLCaps.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGLCaps.h"
 
@@ skipping 1568 matching lines @@
     } else {
         fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fBaseInternalFormat = GR_GL_ALPHA;
         fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_ALPHA8;
         fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fExternalFormat[kOther_ExternalFormatUsage] =
             GR_GL_ALPHA;
         fConfigTable[kAlpha_8_GrPixelConfig].fSwizzle = GrSwizzle::AAAA();
     }
     fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fExternalType = GR_GL_UNSIGNED_BYTE;
     fConfigTable[kAlpha_8_GrPixelConfig].fFormatType = kNormalizedFixedPoint_FormatType;
     fConfigTable[kAlpha_8_GrPixelConfig].fFlags = ConfigInfo::kTextureable_Flag;
-    if (this->textureRedSupport() || kDesktop_ARB_MSFBOType == this->msFBOType()) {
+    if (this->textureRedSupport() ||
+        (kDesktop_ARB_MSFBOType == this->msFBOType() &&
+         ctxInfo.renderer() != kOSMesa_GrGLRenderer)) {
         // desktop ARB extension/3.0+ supports ALPHA8 as renderable.
+        // However, osmesa fails if it used even when GL_ARB_framebuffer_object is present.
         // Core profile removes ALPHA8 support, but we should have chosen R8 in that case.
         fConfigTable[kAlpha_8_GrPixelConfig].fFlags |= allRenderFlags;
     }
     if (texStorageSupported) {
         fConfigTable[kAlpha_8_GrPixelConfig].fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
     }
 
     // Check for [half] floating point texture support
     // NOTE: We disallow floating point textures on ES devices if linear filtering modes are not
     // supported. This is for simplicity, but a more granular approach is possible. Coincidentally,
@@ skipping 302 matching lines @@
         for (int j = 0; j < kExternalFormatUsageCnt; ++j) {
             SkASSERT(defaultEntry.fFormats.fExternalFormat[j] !=
                      fConfigTable[i].fFormats.fExternalFormat[j]);
         }
         SkASSERT(defaultEntry.fFormats.fExternalType != fConfigTable[i].fFormats.fExternalType);
     }
 #endif
 }
 
 void GrGLCaps::onApplyOptionsOverrides(const GrContextOptions& options) {}