Add support for GL_EXT_raster_multisample

src/gpu/gl/GrGLCaps.cpp

Index: src/gpu/gl/GrGLCaps.cpp
diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index d95e10ba64d80d3c53ad73e48e725db38d299161..7af3576dfeca6abbd8b119af722de8a42d0bf5ee 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -306,11 +306,16 @@ void GrGLCaps::init(const GrContextOptions& contextOptions,
         fShaderCaps->pathRenderingSupport()) {
         fUsesMixedSamples = ctxInfo.hasExtension("GL_NV_framebuffer_mixed_samples") ||
                 ctxInfo.hasExtension("GL_CHROMIUM_framebuffer_mixed_samples");
-        // Workaround NVIDIA bug related to glInvalidateFramebuffer and mixed samples.
-        if (fUsesMixedSamples && (kNVIDIA_GrGLDriver == ctxInfo.driver() ||
-                                  kChromium_GrGLDriver == ctxInfo.driver())) {
-            fDiscardRenderTargetSupport = false;
-            fInvalidateFBType = kNone_InvalidateFBType;
+        if (fUsesMixedSamples) {
+            if (kNVIDIA_GrGLDriver == ctxInfo.driver() ||
+                kChromium_GrGLDriver == ctxInfo.driver()) {
+                // Workaround NVIDIA bug related to glInvalidateFramebuffer and mixed samples.
+                fDiscardRenderTargetSupport = false;
+                fInvalidateFBType = kNone_InvalidateFBType;
+            }
+            // Raster multisample is only useful to us when coverage modulation is also supported,
+            // as defined by mixed samples.
+            fRasterMultisampleSupport = ctxInfo.hasExtension("GL_EXT_raster_multisample");
         }
     }
 
@@ -423,11 +428,17 @@ void GrGLCaps::init(const GrContextOptions& contextOptions,
 
     // initFSAASupport() must have been called before this point
     if (GrGLCaps::kES_IMG_MsToTexture_MSFBOType == fMSFBOType) {
-        GR_GL_GetIntegerv(gli, GR_GL_MAX_SAMPLES_IMG, &fMaxColorSampleCount);
+        GR_GL_GetIntegerv(gli, GR_GL_MAX_SAMPLES_IMG, &fMaxStencilSampleCount);
     } else if (GrGLCaps::kNone_MSFBOType != fMSFBOType) {
-        GR_GL_GetIntegerv(gli, GR_GL_MAX_SAMPLES, &fMaxColorSampleCount);
+        GR_GL_GetIntegerv(gli, GR_GL_MAX_SAMPLES, &fMaxStencilSampleCount);
+    }
+    if (fRasterMultisampleSupport) {
+        GR_GL_GetIntegerv(gli, GR_GL_MAX_RASTER_SAMPLES, &fMaxRasterSamples);
+        // This is to guard against platforms that may not support as many samples for
+        // glRasterSamples as they do for framebuffers.
+        fMaxStencilSampleCount = SkTMin(fMaxStencilSampleCount, fMaxRasterSamples);
     }
-    fMaxStencilSampleCount = fMaxColorSampleCount;
+    fMaxColorSampleCount = fMaxStencilSampleCount;
 
     if (kPowerVR54x_GrGLRenderer == ctxInfo.renderer() ||
         kPowerVRRogue_GrGLRenderer == ctxInfo.renderer() ||