Switch fragment coordinate to 'highp' to fix various broken GMs.

src/gpu/glsl/GrGLSLFragmentShaderBuilder.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 "GrGLSLFragmentShaderBuilder.h"
 #include "GrRenderTarget.h"
 #include "glsl/GrGLSL.h"
@@ skipping 128 matching lines @@
         if (!fSetupFragPosition) {
             const char* rtHeightName;
 
             fProgramBuilder->addRTHeightUniform("RTHeight", &rtHeightName);
 
             // The Adreno compiler seems to be very touchy about access to "gl_FragCoord".
             // Accessing glFragCoord.zw can cause a program to fail to link. Additionally,
             // depending on the surrounding code, accessing .xy with a uniform involved can
             // do the same thing. Copying gl_FragCoord.xy into a temp vec2 beforehand 
             // (and only accessing .xy) seems to "fix" things.
-            this->codePrependf("\tvec4 %s = vec4(%s.x, %s - %s.y, 1.0, 1.0);\n",
-                               kCoordName, kTempName, rtHeightName, kTempName);
-            this->codePrependf("vec2 %s = gl_FragCoord.xy;", kTempName);
+            const char* precision = glslCaps->usesPrecisionModifiers() ? "highp " : "";
+            this->codePrependf("\t%svec4 %s = vec4(%s.x, %s - %s.y, 1.0, 1.0);\n",
+                               precision, kCoordName, kTempName, rtHeightName, kTempName);
+            this->codePrependf("%svec2 %s = gl_FragCoord.xy;", precision, kTempName);
             fSetupFragPosition = true;
         }
         SkASSERT(fProgramBuilder->fUniformHandles.fRTHeightUni.isValid());
         return kCoordName;
     }
 }
 
 const char* GrGLSLFragmentShaderBuilder::dstColor() {
     fHasReadDstColor = true;
 
@@ skipping 86 matching lines @@
 }
 
 void GrGLSLFragmentBuilder::onAfterChildProcEmitCode() {
     SkASSERT(fSubstageIndices.count() >= 2);
     fSubstageIndices.pop_back();
     fSubstageIndices.back()++;
     int removeAt = fMangleString.findLastOf('_');
     fMangleString.remove(removeAt, fMangleString.size() - removeAt);
 }