Fix edge-line artifacts issue on Mali

src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrGLVertexShaderBuilder.h"
 #include "GrGLProgramBuilder.h"
 #include "../GrGLGpu.h"
@@ skipping 18 matching lines @@
     int vaCount = gp.numAttribs();
     for (int i = 0; i < vaCount; i++) {
         this->addAttribute(&gp.getAttrib(i));
     }
     return;
 }
 
 void GrGLVertexBuilder::transformToNormalizedDeviceSpace(const GrShaderVar& posVar) {
     SkASSERT(!fRtAdjustName);
 
+    GrSLPrecision precision = kDefault_GrSLPrecision;
+    if (fProgramBuilder->ctxInfo().vendor() == kARM_GrGLVendor) {
+        precision = kHigh_GrSLPrecision;
+    }
+
     // setup RT Uniform
     fProgramBuilder->fUniformHandles.fRTAdjustmentUni =
             fProgramBuilder->addUniform(GrGLProgramBuilder::kVertex_Visibility,
-                                        kVec4f_GrSLType, kDefault_GrSLPrecision,
+                                        kVec4f_GrSLType, precision,
                                         fProgramBuilder->rtAdjustment(),
                                         &fRtAdjustName);
     if (this->getProgramBuilder()->desc().header().fSnapVerticesToPixelCenters) {
         if (kVec3f_GrSLType == posVar.getType()) {
             const char* p = posVar.c_str();
             this->codeAppendf("{vec2 _posTmp = vec2(%s.x/%s.z, %s.y/%s.z);", p, p, p, p);
         } else {
             SkASSERT(kVec2f_GrSLType == posVar.getType());
             this->codeAppendf("{vec2 _posTmp = %s;", posVar.c_str());
         }
@@ skipping 40 matching lines @@
     for (int i = 0; i < fInputs.count(); ++i) {
         const GrGLShaderVar& attr = fInputs[i];
         // if attribute already added, don't add it again
         if (attr.getName().equals(var.getName())) {
             return false;
         }
     }
     fInputs.push_back(var);
     return true;
 }