Make SkOSWindow return the sample count and stencil bit count for its GL context.

include/views/SkOSWindow_Win.h

Index: include/views/SkOSWindow_Win.h
===================================================================
--- include/views/SkOSWindow_Win.h	(revision 7991)
+++ include/views/SkOSWindow_Win.h	(working copy)
@@ -37,7 +37,12 @@
 #endif // SK_SUPPORT_GPU
     };
 
-    bool attach(SkBackEndTypes attachType, int msaaSampleCount);
+    struct AttachmentInfo {
+        int fSampleCount;
+        int fStencilBits;
+    };
+
+    bool attach(SkBackEndTypes attachType, int msaaSampleCount, AttachmentInfo*);
     void detach();
     void present();
 
@@ -70,6 +75,7 @@
     EGLDisplay          fDisplay;
     EGLContext          fContext;
     EGLSurface          fSurface;
+    EGLConfig           fConfig;
 #endif // SK_ANGLE
 #endif // SK_SUPPORT_GPU
 
@@ -78,12 +84,12 @@
     SkBackEndTypes      fAttached;
 
 #if SK_SUPPORT_GPU
-    bool attachGL(int msaaSampleCount);
+    bool attachGL(int msaaSampleCount, AttachmentInfo* info);
     void detachGL();
     void presentGL();
 
 #if SK_ANGLE
-    bool attachANGLE(int msaaSampleCount);
+    bool attachANGLE(int msaaSampleCount, AttachmentInfo* info);
     void detachANGLE();
     void presentANGLE();
 #endif // SK_ANGLE