Reland of Untouch out of bound pixels for CopyTexSubImage2D

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 515a825aaedef5a4becfea456eb0212b8aa51679..7a1bbf69d3f2e68e0f96f6dc2b477cdd669f7232 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -11397,26 +11397,6 @@ void GLES2DecoderImpl::DoCopyTexSubImage2D(
     texture_manager()->SetLevelCleared(texture_ref, target, level, true);
   }
 
-  if (copyX != x ||
-      copyY != y ||
-      copyWidth != width ||
-      copyHeight != height) {
-    // some part was clipped so clear the sub rect.
-    uint32_t pixels_size = 0;
-    if (!GLES2Util::ComputeImageDataSizes(
-        width, height, 1, format, type, state_.unpack_alignment, &pixels_size,
-        NULL, NULL)) {
-      LOCAL_SET_GL_ERROR(
-          GL_INVALID_VALUE, "glCopyTexSubImage2D", "dimensions too large");
-      return;
-    }
-    scoped_ptr<char[]> zero(new char[pixels_size]);
-    memset(zero.get(), 0, pixels_size);
-    glTexSubImage2D(
-        target, level, xoffset, yoffset, width, height,
-        format, type, zero.get());
-  }

[Zhenyao Mo, 2016/01/14 18:13:37]

Look at the code above SetLevelClearedRect(), since now we leave out-of-bounds
pixels untouched, then we need to take that into consideration for the cleared
rect. Otherwise we could end up leaking vram.

[qiankun, 2016/01/19 16:07:31]

Thanks for pointing this. I updated the CL. PTAL. 

-
   if (copyHeight > 0 && copyWidth > 0) {
     GLint dx = copyX - x;
     GLint dy = copyY - y;