Ensured that texture completeness takes into account base and max level

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 20b3fb72338e2e11a8f9f08a55739161f32eb892..caeed8a2f1ec3100fa25eada5eab1d143f3614bf 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -4999,7 +4999,31 @@ void GLES2DecoderImpl::DoGenerateMipmap(GLenum target) {
   if (workarounds().set_texture_filter_before_generating_mipmap) {
     glTexParameteri(target, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_NEAREST);
   }
+
+  // Workaround for Mac driver bug. If the base level is non-zero but the zero
+  // level of a texture has not been set glGenerateMipmaps sets the entire mip
+  // chain to opaque black. If the zero level is set at all, however, the mip
+  // chain is properly generated from the base level.
+  bool texture_zero_level_set = false;
+  GLenum type, internal_format, format;
+  if (workarounds().set_zero_level_before_generating_mipmap &&
+      target == GL_TEXTURE_2D) {
+    Texture* tex = texture_ref->texture();
+    if (tex && tex->base_level() != 0 &&
+        !tex->GetLevelType(target, 0, &type, &internal_format) &&
+        tex->GetLevelType(target, tex->base_level(), &type, &internal_format)) {

[zmo, 2015/11/23 23:14:47]

nit: the last condition is unnecessary because CanGenerateMipmaps() above should
already make sure it always returns true.

+      format = TextureManager::ExtractFormatFromStorageFormat(internal_format);
+      glTexImage2D(target, 0, internal_format, 1, 1, 0, format, type, nullptr);
+      texture_zero_level_set = true;
+    }
+  }
+
   glGenerateMipmapEXT(target);
+
+  if (texture_zero_level_set) {
+    glTexImage2D(target, 0, internal_format, 0, 0, 0, format, type, nullptr);

[zmo, 2015/11/23 23:14:47]

Could you please add a note that this might have side effects because the
texture level might have switched from uninitialized to initialized to size(0,
0) , but hopefully command buffer will intercept most calls that are affected?

+  }
+
   if (workarounds().set_texture_filter_before_generating_mipmap) {
     glTexParameteri(target, GL_TEXTURE_MIN_FILTER,
                     texture_ref->texture()->min_filter());