Fix edge-line artifacts issue on Mali

src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp

Index: src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp
diff --git a/src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp b/src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp
index f484497954992e47e71f6e269b39e41d6727eb90..6d5d344088d1671fc410bd3793e6813966b834bf 100644
--- a/src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp
@@ -36,10 +36,15 @@ void GrGLVertexBuilder::emitAttributes(const GrGeometryProcessor& gp) {
 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) {