Fix immutable tex srgb emulation issue of generateMipmap

gpu/command_buffer/service/gles2_cmd_srgb_converter.cc

Index: gpu/command_buffer/service/gles2_cmd_srgb_converter.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_srgb_converter.cc b/gpu/command_buffer/service/gles2_cmd_srgb_converter.cc
index 97201e637eee586e2447cf1876a874a21246bb63..bf22d0e40ec698f034b60600f7db59d5bd9c849b 100644
--- a/gpu/command_buffer/service/gles2_cmd_srgb_converter.cc
+++ b/gpu/command_buffer/service/gles2_cmd_srgb_converter.cc
@@ -415,8 +415,13 @@ void SRGBConverter::GenerateMipmap(const gles2::GLES2Decoder* decoder,
   tex->GetLevelSize(target, base_level, &width, &height, &depth);
   tex->GetLevelType(target, base_level, &type, &internal_format);
   format = TextureManager::ExtractFormatFromStorageFormat(internal_format);
-  const GLint mipmap_levels =
-      TextureManager::ComputeMipMapCount(target, width, height, depth);
+  GLint mipmap_levels;
+  if (tex->IsImmutable()) {
+    mipmap_levels = tex->GetImmutableLevels();
+  } else {
+    mipmap_levels =
+        TextureManager::ComputeMipMapCount(target, width, height, depth);
+  }
 
   glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[1]);
   if (feature_info_->ext_color_buffer_float_available() &&
@@ -458,8 +463,9 @@ void SRGBConverter::GenerateMipmap(const gles2::GLES2Decoder* decoder,
   glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[1]);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
                   GL_NEAREST_MIPMAP_NEAREST);
-  width >>= 1;
-  height >>= 1;
+
+  width = (width == 1) ? 1 : width >> 1;
+  height = (height == 1) ? 1 : height >> 1;
 
   // TODO(yizhou): An optimization. Attach 1 level at a time, once for every
   // iteration of the loop.
@@ -468,16 +474,18 @@ void SRGBConverter::GenerateMipmap(const gles2::GLES2Decoder* decoder,
     // copy mipmaps level by level from srgb_converter_textures_[1] to tex
     // generate mipmap for tex manually
     glBindTexture(GL_TEXTURE_2D, tex->service_id());
-    glTexImage2D(GL_TEXTURE_2D, level, internal_format, width, height, 0,
-                 format, type, nullptr);
+    if (!tex->IsImmutable()) {
+      glTexImage2D(GL_TEXTURE_2D, level, internal_format, width, height, 0,
+                   format, type, nullptr);
+    }
     glFramebufferTexture2DEXT(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                               GL_TEXTURE_2D, tex->service_id(), level);
 
     glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[1]);
     glViewport(0, 0, width, height);
     glDrawArrays(GL_TRIANGLES, 0, 6);
-    width >>= 1;
-    height >>= 1;
+    width = (width == 1) ? 1 : width >> 1;
+    height = (height == 1) ? 1 : height >> 1;
   }
 
   // Restore state