fixup precision with configurable atlas

src/gpu/effects/GrDistanceFieldGeoProc.cpp

Index: src/gpu/effects/GrDistanceFieldGeoProc.cpp
diff --git a/src/gpu/effects/GrDistanceFieldGeoProc.cpp b/src/gpu/effects/GrDistanceFieldGeoProc.cpp
index 0b97bb2b94980b225dd2ed7186b6cd70d4f1a4e1..d8fbd86cb33052a439e2c53d496c5b0224e60354 100755
--- a/src/gpu/effects/GrDistanceFieldGeoProc.cpp
+++ b/src/gpu/effects/GrDistanceFieldGeoProc.cpp
@@ -80,15 +80,15 @@ public:
         // compute numbers to be hardcoded to convert texture coordinates from int to float
         SkASSERT(dfTexEffect.numTextures() == 1);
         GrTexture* atlas = dfTexEffect.textureAccess(0).getTexture();
-        SkASSERT(atlas);
+        SkASSERT(atlas && SkIsPow2(atlas->width()) && SkIsPow2(atlas->height()));
         SkScalar recipWidth = 1.0f / atlas->width();
         SkScalar recipHeight = 1.0f / atlas->height();
 
         GrGLVertToFrag uv(kVec2f_GrSLType);
         args.fPB->addVarying("TextureCoords", &uv, kHigh_GrSLPrecision);
         vsBuilder->codeAppendf("%s = vec2(%.*f, %.*f) * %s;", uv.vsOut(),
-                               SK_FLT_DECIMAL_DIG, recipWidth,
-                               SK_FLT_DECIMAL_DIG, recipHeight,
+                               GR_SIGNIFICANT_POW2_DECIMAL_DIG, recipWidth,
+                               GR_SIGNIFICANT_POW2_DECIMAL_DIG, recipHeight,
                                dfTexEffect.inTextureCoords()->fName);
         
         // Use highp to work around aliasing issues
@@ -542,15 +542,15 @@ public:
         // compute numbers to be hardcoded to convert texture coordinates from int to float
         SkASSERT(dfTexEffect.numTextures() == 1);
         GrTexture* atlas = dfTexEffect.textureAccess(0).getTexture();
-        SkASSERT(atlas);
+        SkASSERT(atlas && SkIsPow2(atlas->width()) && SkIsPow2(atlas->height()));
         SkScalar recipWidth = 1.0f / atlas->width();
         SkScalar recipHeight = 1.0f / atlas->height();
 
         GrGLVertToFrag uv(kVec2f_GrSLType);
         args.fPB->addVarying("TextureCoords", &uv, kHigh_GrSLPrecision);
         vsBuilder->codeAppendf("%s = vec2(%.*f, %.*f) * %s;", uv.vsOut(),
-                               SK_FLT_DECIMAL_DIG, recipWidth,
-                               SK_FLT_DECIMAL_DIG, recipHeight,
+                               GR_SIGNIFICANT_POW2_DECIMAL_DIG, recipWidth,
+                               GR_SIGNIFICANT_POW2_DECIMAL_DIG, recipHeight,
                                dfTexEffect.inTextureCoords()->fName);
 
         // add frag shader code