Add API for GrContext to recommend rendertarget sample count

src/gpu/GrContext.cpp

Index: src/gpu/GrContext.cpp
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index bb0f4fa9fab3ee573311c91a219f9ab9abb98aca..aa31a3b0ba7760837044be1ff71233d3e38d090e 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -1703,6 +1703,15 @@ bool GrContext::isConfigRenderable(GrPixelConfig config, bool withMSAA) const {
     return fGpu->caps()->isConfigRenderable(config, withMSAA);
 }
 
+int GrContext::getRecommendedSampleCount(GrPixelConfig config, float) const {
+  if (this->isConfigRenderable(config, true)) {
+    if (fGpu->caps()->pathRenderingSupport()) {
+      return 4;

[bsalomon, 2014/03/06 14:02:43]

Should probably also check that 4 >= caps()->maxSampleCount().

I'm thinking that we may want to check the DPI and go to 16 samples on a typical
"desktop" display. Maybe if we're below 250 dpi? I'm sure what the right
threshold is but I think 4 samples will look bad on a standard monitor. (Maybe
in the future someone can do some experimentation and fine tune it and perhaps
figure out if it makes sense to have an 8 sample middle ground as well.)

+    }
+  }
+  return 0;
+}
+
 void GrContext::setupDrawBuffer() {
     SkASSERT(NULL == fDrawBuffer);
     SkASSERT(NULL == fDrawBufferVBAllocPool);