Use mapped memory for uploading large textures.

gpu/command_buffer/client/ring_buffer.cc

Index: gpu/command_buffer/client/ring_buffer.cc
diff --git a/gpu/command_buffer/client/ring_buffer.cc b/gpu/command_buffer/client/ring_buffer.cc
index 813bb348863d8810c93690896a9441c67e194c79..bf848a22199bc27903aecc786486de91150114ff 100644
--- a/gpu/command_buffer/client/ring_buffer.cc
+++ b/gpu/command_buffer/client/ring_buffer.cc
@@ -103,6 +103,27 @@ void RingBuffer::FreePendingToken(void* pointer,
   NOTREACHED() << "attempt to free non-existant block";
 }
 
+void RingBuffer::DiscardBlock(void* pointer) {
+  Offset offset = GetOffset(pointer);
+  offset -= base_offset_;
+  DCHECK(!blocks_.empty()) << "no allocations to free";
+  for (Container::reverse_iterator it = blocks_.rbegin();
+        it != blocks_.rend();
+        ++it) {
+    Block& block = *it;
+    if (block.offset == offset) {
+      DCHECK(block.state == IN_USE)
+          << "block that corresponds to offset already freed";
+
+      // Mark this as padding and let the FreeOldestBlock() logic handle
+      // updating all the various offsets.
+      block.state = PADDING;
+      return;
+    }
+  }
+  NOTREACHED() << "attempt to free non-existant block";
+}
+
 unsigned int RingBuffer::GetLargestFreeSizeNoWaiting() {
   unsigned int last_token_read = helper_->last_token_read();
   while (!blocks_.empty()) {