command buffers: correctly handle Flush(num_entries)

CommandBufferService should not accept put == num_entries, the client must
wraparound to 0 (CommandBufferHelper does).
CommandParser wraps to 0 and never sets get_ == num_entries, so
CommandParser::IsEmpty would never become true.

A test should have caught that but unfortunately it confused buffer size and
number of entries. This fixes it.

BUG=None
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2304813002
Cr-Commit-Position: refs/heads/master@{#417211}

gpu/command_buffer/service/command_buffer_service.cc

@@ -87,7 +87,7 @@ void CommandBufferService::WaitForGetOffsetInRange(int32_t start, int32_t end) {
 }
 
 void CommandBufferService::Flush(int32_t put_offset) {
-  if (put_offset < 0 || put_offset > num_entries_) {
+  if (put_offset < 0 || put_offset >= num_entries_) {
     error_ = gpu::error::kOutOfBounds;
     return;
   }

gpu/command_buffer/service/command_buffer_service_unittest.cc

@@ -45,7 +45,8 @@ class CommandBufferServiceTest : public testing::Test {
 
   int32_t GetError() { return command_buffer_->GetLastState().error; }
 
-  bool Initialize(size_t size) {
+  bool Initialize(size_t entries) {
+    size_t size = entries * sizeof(CommandBufferEntry);
     int32_t id;
     command_buffer_->CreateTransferBuffer(size, &id);
     EXPECT_GT(id, 0);