Share Group plumbing in Blink; Remove WebGL from 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 8b3bd008303b195f7fdd492ce4be180db5346f18..5e917ce3ea3fa8d8514c64ff11c1ca929f1bb28a 100644
--- a/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -329,14 +329,33 @@ bool DrawingBuffer::copyToPlatformTexture(blink::WebGraphicsContext3D* context,
         }
         m_context->flush();
     }
-    Platform3DObject sourceTexture = m_colorBuffer;
 
-    if (!context->makeContextCurrent())
+    if (!Extensions3DUtil::canUseCopyTextureCHROMIUM(internalFormat, destType, level))
         return false;
 
-    if (!Extensions3DUtil::canUseCopyTextureCHROMIUM(internalFormat, destType, level))
+    // Contexts may be in a different share group. We must transfer the texture through a mailbox first
+    RefPtr<MailboxInfo> bufferMailbox = adoptRef(new MailboxInfo());
+    m_context->genMailboxCHROMIUM(bufferMailbox->mailbox.name);
+    m_context->bindTexture(GL_TEXTURE_2D, m_colorBuffer);
+    m_context->produceTextureCHROMIUM(GL_TEXTURE_2D, bufferMailbox->mailbox.name);
+    m_context->flush();
+
+    bufferMailbox->mailbox.syncPoint = m_context->insertSyncPoint();
+
+    if (!context->makeContextCurrent())
         return false;
 
+    Platform3DObject sourceTexture = context->createTexture();
+
+    // TODO(bajones): Should be able to change the texture bindings here without reverting but
+    // something else in the system is depending on it. Failing to revert causes WebGL
+    // tests to fail. We should find out why and fix it.
+    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);
+
     bool unpackPremultiplyAlphaNeeded = false;
     bool unpackUnpremultiplyAlphaNeeded = false;
     if (m_attributes.alpha && m_attributes.premultipliedAlpha && !premultiplyAlpha)
@@ -351,7 +370,12 @@ bool DrawingBuffer::copyToPlatformTexture(blink::WebGraphicsContext3D* context,
     context->pixelStorei(GC3D_UNPACK_FLIP_Y_CHROMIUM, false);
     context->pixelStorei(GC3D_UNPACK_UNPREMULTIPLY_ALPHA_CHROMIUM, false);
     context->pixelStorei(GC3D_UNPACK_PREMULTIPLY_ALPHA_CHROMIUM, false);
+
+    context->bindTexture(GL_TEXTURE_2D, boundTexture);
+    context->deleteTexture(sourceTexture);
+
     context->flush();
+    m_context->waitSyncPoint(context->insertSyncPoint());
 
     return true;
 }