Allow the renderer process to map textures from one context into another.

gpu/command_buffer/service/gpu_scheduler.cc

Index: gpu/command_buffer/service/gpu_scheduler.cc
===================================================================
--- gpu/command_buffer/service/gpu_scheduler.cc	(revision 94701)
+++ gpu/command_buffer/service/gpu_scheduler.cc	(working copy)
@@ -129,6 +129,18 @@
     return decoder_->SetParent(NULL, 0);
 }
 
+bool GpuScheduler::MapExternalResource(
+    resource_type::ResourceType resource_type,
+    uint32 resource_source_id,
+    GpuScheduler* source_scheduler,
+    uint32 resource_dest_id) {
+  return decoder_->MapExternalResource(
+      resource_type,
+      resource_source_id,
+      source_scheduler ? source_scheduler->decoder_.get() : NULL,
+      resource_dest_id);
+}
+
 #if defined(OS_MACOSX)
 namespace {
 const unsigned int kMaxOutstandingSwapBuffersCallsPerOnscreenContext = 1;