Fix the remaining issue of seperating WebGL from the default share group

Source/platform/graphics/gpu/DrawingBuffer.cpp

Index: Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/Source/platform/graphics/gpu/DrawingBuffer.cpp b/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 2a94073d841986f585b0578d3be041b986e2b074..a38cb2b2cac0860b50ab7694fe8406265a334b56 100644
--- a/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -41,6 +41,7 @@
 #include "public/platform/WebExternalBitmap.h"
 #include "public/platform/WebExternalTextureLayer.h"
 #include "public/platform/WebGraphicsContext3D.h"
+#include "public/platform/WebGraphicsContext3DProvider.h"
 
 using namespace std;
 
@@ -411,9 +412,33 @@ void DrawingBuffer::paintCompositedResultsToCanvas(ImageBuffer* imageBuffer)
         return;
     Platform3DObject tex = imageBuffer->getBackingTexture();
     if (tex) {
-        m_context->copyTextureCHROMIUM(GL_TEXTURE_2D, m_frontColorBuffer,
-            tex, 0, GL_RGBA, GL_UNSIGNED_BYTE);
+        RefPtr<MailboxInfo> bufferMailbox = adoptRef(new MailboxInfo());
+        m_context->genMailboxCHROMIUM(bufferMailbox->mailbox.name);
+        m_context->bindTexture(GL_TEXTURE_2D, m_frontColorBuffer);
+        m_context->produceTextureCHROMIUM(GL_TEXTURE_2D, bufferMailbox->mailbox.name);
         m_context->flush();
+
+        bufferMailbox->mailbox.syncPoint = m_context->insertSyncPoint();
+        OwnPtr<blink::WebGraphicsContext3DProvider> provider =
+            adoptPtr(blink::Platform::current()->createSharedOffscreenGraphicsContext3DProvider());
+        if (!provider)
+            return;
+        blink::WebGraphicsContext3D* context = provider->context3d();
+        if (!context || !context->makeContextCurrent())
+            return;
+
+        Platform3DObject sourceTexture = context->createTexture();
+        GLint boundTexture = 0;
+        context->getIntegerv(GL_TEXTURE_BINDING_2D, &boundTexture);
+        context->bindTexture(GL_TEXTURE_2D, sourceTexture);
+        context->waitSyncPoint(bufferMailbox->mailbox.syncPoint);
+        context->consumeTextureCHROMIUM(GL_TEXTURE_2D, bufferMailbox->mailbox.name);
+        context->copyTextureCHROMIUM(GL_TEXTURE_2D, sourceTexture,
+            tex, 0, GL_RGBA, GL_UNSIGNED_BYTE);
+        context->bindTexture(GL_TEXTURE_2D, boundTexture);
+        context->deleteTexture(sourceTexture);
+        context->flush();
+        m_context->waitSyncPoint(context->insertSyncPoint());
         return;
     }