Suppress handle leaks under WebGraphicsContext3DCommandBufferImpl.

BUG=481305
TBR=emircan@chromium.org,hanxi@chromium.org

Review URL: https://codereview.chromium.org/1085323004

Cr-Commit-Position: refs/heads/master@{#326958}

tools/valgrind/drmemory/suppressions_full.txt

@@ -1937,3 +1937,15 @@ base.dll!base::SharedMemory::ShareToProcessCommon
 gl_wrapper.dll!gfx::GLImageSharedMemory::Initialize
 content.dll!content::GpuChannel::CreateImageForGpuMemoryBuffer
 content.dll!content::GpuCommandBufferStub::OnCreateImage
+
+HANDLE LEAK
+name=https://crbug.com/481305
+system call NtCreateSection
+KERNELBASE.dll!CreateFileMappingW
+base.dll!base::SharedMemory::Create
+base.dll!base::SharedMemory::CreateAnonymous
+content.dll!content::ChildThreadImpl::AllocateSharedMemory
+content.dll!content::RenderThreadImpl::HostAllocateSharedMemoryBuffer
+content.dll!content::RenderThreadImpl::AllocateSharedMemory
+...
+content.dll!content::WebGraphicsContext3DCommandBufferImpl::CreateContext