Refine the Attachment completeness check on WebGLFramebuffer.
It fixes the issue that fails to catch several incompleteness cases and adds more detailed report on the reason of framebuffer incompleteness.
  
BUG=260690

Review URL: https://chromiumcodereview.appspot.com/19272013

git-svn-id: svn://svn.chromium.org/blink/trunk@155763 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Increase separation between CSSValue conversion and setting of RenderStyles in StyleBuilder

This patch allows us to write functions which convert CSSValues to types
appropriate for RenderStyles, while leaving the actual calling of the
setter to the generated code. Some of the motivation here includes
making the SVG properties easier to move across, making more of the type
information in the .in file correct (this will be useful for some of the
AnimatableValue work going on in the animations rewrite) and making it
clearer whether custom handlers are doing more than just conversions.
The converters here are similar to what currently exists in the file
CSSPrimitiveValueMappings, although we won't necessarily restrict us to
CSSPrimitiveValues.
I'm a bit wary of adding (C++) templated converter functions, but these
are all short and seem easy to understand.

BUG=237400

Review URL: https://chromiumcodereview.appspot.com/21470002

git-svn-id: svn://svn.chromium.org/blink/trunk@155764 bbb929c8-8fbe-4397-9dbb-9b2b20218538