Add discard API to SkCanvas, plumb it to glDiscardFramebuffer()

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 a60230a2fe91de7e744a27a002cac988e6b3f912..f21506b20e7d356f9b2c14b842b6894853acedb2 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -45,7 +45,6 @@ void GrGLCaps::reset() {
     fUseNonVBOVertexAndIndexDynamicData = false;
     fIsCoreProfile = false;
     fFixedFunctionSupport = false;
-    fDiscardFBSupport = false;
     fFullClearIsFree = false;
 }
 
@@ -82,7 +81,6 @@ GrGLCaps& GrGLCaps::operator = (const GrGLCaps& caps) {
     fUseNonVBOVertexAndIndexDynamicData = caps.fUseNonVBOVertexAndIndexDynamicData;
     fIsCoreProfile = caps.fIsCoreProfile;
     fFixedFunctionSupport = caps.fFixedFunctionSupport;
-    fDiscardFBSupport = caps.fDiscardFBSupport;
     fFullClearIsFree = caps.fFullClearIsFree;
 
     return *this;
@@ -222,7 +220,7 @@ void GrGLCaps::init(const GrGLContextInfo& ctxInfo, const GrGLInterface* gli) {
         fUseNonVBOVertexAndIndexDynamicData = true;
     }
 
-    fDiscardFBSupport = ctxInfo.hasExtension("GL_EXT_discard_framebuffer");
+    fDiscardRenderTargetSupport = ctxInfo.hasExtension("GL_EXT_discard_framebuffer");
 
     if (kARM_GrGLVendor == ctxInfo.vendor() || kImagination_GrGLVendor == ctxInfo.vendor()) {
         fFullClearIsFree = true;
@@ -659,7 +657,6 @@ SkString GrGLCaps::dump() const {
     r.appendf("Vertex array object support: %s\n", (fVertexArrayObjectSupport ? "YES": "NO"));
     r.appendf("Use non-VBO for dynamic data: %s\n",
              (fUseNonVBOVertexAndIndexDynamicData ? "YES" : "NO"));
-    r.appendf("Discard FrameBuffer support: %s\n", (fDiscardFBSupport ? "YES" : "NO"));
     r.appendf("Full screen clear is free: %s\n", (fFullClearIsFree ? "YES" : "NO"));
     return r;
 }