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

src/gpu/GrDrawTarget.cpp

Index: src/gpu/GrDrawTarget.cpp
diff --git a/src/gpu/GrDrawTarget.cpp b/src/gpu/GrDrawTarget.cpp
index 8d3ded2d65c82f33307041a013787c048b562365..10698442b258b5f556f1243bd7b998b2e84d1ee2 100644
--- a/src/gpu/GrDrawTarget.cpp
+++ b/src/gpu/GrDrawTarget.cpp
@@ -1019,6 +1019,7 @@ void GrDrawTargetCaps::reset() {
     fBufferLockSupport = false;
     fPathRenderingSupport = false;
     fDstReadInShaderSupport = false;
+    fDiscardRenderTargetSupport = false;
     fReuseScratchTextures = true;
     fGpuTracingSupport = false;
 
@@ -1042,6 +1043,7 @@ GrDrawTargetCaps& GrDrawTargetCaps::operator=(const GrDrawTargetCaps& other) {
     fBufferLockSupport = other.fBufferLockSupport;
     fPathRenderingSupport = other.fPathRenderingSupport;
     fDstReadInShaderSupport = other.fDstReadInShaderSupport;
+    fDiscardRenderTargetSupport = other.fDiscardRenderTargetSupport;
     fReuseScratchTextures = other.fReuseScratchTextures;
     fGpuTracingSupport = other.fGpuTracingSupport;
 
@@ -1057,23 +1059,24 @@ GrDrawTargetCaps& GrDrawTargetCaps::operator=(const GrDrawTargetCaps& other) {
 SkString GrDrawTargetCaps::dump() const {
     SkString r;
     static const char* gNY[] = {"NO", "YES"};
-    r.appendf("8 Bit Palette Support       : %s\n", gNY[f8BitPaletteSupport]);
-    r.appendf("MIP Map Support             : %s\n", gNY[fMipMapSupport]);
-    r.appendf("NPOT Texture Tile Support   : %s\n", gNY[fNPOTTextureTileSupport]);
-    r.appendf("Two Sided Stencil Support   : %s\n", gNY[fTwoSidedStencilSupport]);
-    r.appendf("Stencil Wrap Ops  Support   : %s\n", gNY[fStencilWrapOpsSupport]);
-    r.appendf("HW AA Lines Support         : %s\n", gNY[fHWAALineSupport]);
-    r.appendf("Shader Derivative Support   : %s\n", gNY[fShaderDerivativeSupport]);
-    r.appendf("Geometry Shader Support     : %s\n", gNY[fGeometryShaderSupport]);
-    r.appendf("Dual Source Blending Support: %s\n", gNY[fDualSourceBlendingSupport]);
-    r.appendf("Buffer Lock Support         : %s\n", gNY[fBufferLockSupport]);
-    r.appendf("Path Rendering Support      : %s\n", gNY[fPathRenderingSupport]);
-    r.appendf("Dst Read In Shader Support  : %s\n", gNY[fDstReadInShaderSupport]);
-    r.appendf("Reuse Scratch Textures      : %s\n", gNY[fReuseScratchTextures]);
-    r.appendf("Gpu Tracing Support         : %s\n", gNY[fGpuTracingSupport]);
-    r.appendf("Max Texture Size            : %d\n", fMaxTextureSize);
-    r.appendf("Max Render Target Size      : %d\n", fMaxRenderTargetSize);
-    r.appendf("Max Sample Count            : %d\n", fMaxSampleCount);
+    r.appendf("8 Bit Palette Support        : %s\n", gNY[f8BitPaletteSupport]);
+    r.appendf("MIP Map Support              : %s\n", gNY[fMipMapSupport]);
+    r.appendf("NPOT Texture Tile Support    : %s\n", gNY[fNPOTTextureTileSupport]);
+    r.appendf("Two Sided Stencil Support    : %s\n", gNY[fTwoSidedStencilSupport]);
+    r.appendf("Stencil Wrap Ops  Support    : %s\n", gNY[fStencilWrapOpsSupport]);
+    r.appendf("HW AA Lines Support          : %s\n", gNY[fHWAALineSupport]);
+    r.appendf("Shader Derivative Support    : %s\n", gNY[fShaderDerivativeSupport]);
+    r.appendf("Geometry Shader Support      : %s\n", gNY[fGeometryShaderSupport]);
+    r.appendf("Dual Source Blending Support : %s\n", gNY[fDualSourceBlendingSupport]);
+    r.appendf("Buffer Lock Support          : %s\n", gNY[fBufferLockSupport]);
+    r.appendf("Path Rendering Support       : %s\n", gNY[fPathRenderingSupport]);
+    r.appendf("Dst Read In Shader Support   : %s\n", gNY[fDstReadInShaderSupport]);
+    r.appendf("Discard Render Target Support: %s\n", gNY[fDiscardRenderTargetSupport]);
+    r.appendf("Reuse Scratch Textures       : %s\n", gNY[fReuseScratchTextures]);
+    r.appendf("Gpu Tracing Support          : %s\n", gNY[fGpuTracingSupport]);
+    r.appendf("Max Texture Size             : %d\n", fMaxTextureSize);
+    r.appendf("Max Render Target Size       : %d\n", fMaxRenderTargetSize);
+    r.appendf("Max Sample Count             : %d\n", fMaxSampleCount);
 
     static const char* kConfigNames[] = {
         "Unknown",  // kUnknown_GrPixelConfig