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..1c60f688b9184e77d4d893480486cbbbdb6f7ca7 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -1703,6 +1703,21 @@ bool GrContext::isConfigRenderable(GrPixelConfig config, bool withMSAA) const {
     return fGpu->caps()->isConfigRenderable(config, withMSAA);
 }
 
+int GrContext::getRecommendedSampleCount(GrPixelConfig config, SkScalar dpi) const {
+    if (!this->isConfigRenderable(config, true)) {
+        return 0;
+    }
+    int chosenSampleCount = 0;
+    if (fGpu->caps()->pathRenderingSupport()) {
+        if (dpi >= 250.0f) {
+            chosenSampleCount = 4;
+        } else {
+            chosenSampleCount = 16;
+        }
+    }
+    return GrMin(fGpu->caps()->maxSampleCount(), chosenSampleCount);

[bsalomon, 2014/03/07 18:35:36]

maybe:

return chosenSampleCount < fGpu->caps()->maxSampleCount() ? chosenSampleCount :
0

?

I think we should not recommend MSAA if we can't meet some min AA quality bar.

Otherwise lgtm (feel free to update and check CQ if you're ok with the
suggestion).

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