Fix float and half float support on mobile.

src/gpu/gl/GrGpuGL.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGpuGL.h"
 #include "GrGLStencilBuffer.h"
@@ skipping 2224 matching lines @@
             *internalFormat = GR_GL_COMPRESSED_RGBA_ASTC_12x12;
             break;
 
         case kRGBA_float_GrPixelConfig:
             *internalFormat = GR_GL_RGBA32F;
             *externalFormat = GR_GL_RGBA;
             *externalType = GR_GL_FLOAT;
             break;
 
         case kAlpha_half_GrPixelConfig:
-            if (this->glCaps().textureRedSupport()) {
+            if (kGLES_GrGLStandard == this->glStandard() && this->glVersion() < GR_GL_VER(3, 1)) {
+                *internalFormat = GR_GL_ALPHA;
+                *externalFormat = GR_GL_ALPHA;
+                *externalType = GR_GL_HALF_FLOAT_OES;
+            } else if (this->glCaps().textureRedSupport()) {
                 *internalFormat = GR_GL_R16F;
                 *externalFormat = GR_GL_RED;
-                *externalType = (kGLES_GrGLStandard == this->glStandard()) ? GR_GL_HALF_FLOAT
-                                                                           : GR_GL_HALF_FLOAT_OES;
+                *externalType = GR_GL_HALF_FLOAT;
             } else {
                 *internalFormat = GR_GL_ALPHA16F;
                 *externalFormat = GR_GL_ALPHA;
-                *externalType = (kGLES_GrGLStandard == this->glStandard()) ? GR_GL_HALF_FLOAT
-                                                                           : GR_GL_HALF_FLOAT_OES;
+                *externalType = GR_GL_HALF_FLOAT;
             }
             break;
             
         default:
             return false;
     }
     return true;
 }
 
 void GrGpuGL::setTextureUnit(int unit) {
@@ skipping 318 matching lines @@
             this->setVertexArrayID(gpu, 0);
         }
         int attrCount = gpu->glCaps().maxVertexAttributes();
         if (fDefaultVertexArrayAttribState.count() != attrCount) {
             fDefaultVertexArrayAttribState.resize(attrCount);
         }
         attribState = &fDefaultVertexArrayAttribState;
     }
     return attribState;
 }