Revert of Use Shadow DOM to display fallback content for images (patchset #28 id:540001 of https://codereview.chromium.org/481753002/)

Reason for revert:
Broke accessibility tests on Chrome build

Original issue's description:
> This replaces the use of painting in RenderImage to display an image's alt text
> with an implementation in shadow DOM. This initial implementation is close in
> appearance to the legacy display of alt-text but will ultimately move closer to
> the one seen in Firefox and described in http://hixie.ch/specs/alttext.
> 
> The alt-text and broken-image icon is now rendered as:
> 
>     <style>
>         #alttext-container {
>         overflow: hidden;
>         border: 1px solid silver;
>         padding: 1px;          
>         display: inline-block;        
>         }                                 
>         #alttext { display: none; overflow: hidden;}
>     </style>                                    
>     <div id="alttext-container">                  
>         <img src="data:png, [broken-image-icon]" width="16" height="16" align="left" style="margin: 0px">
>         <div id="alt-text">Alt text in here</div>         
>     </div>                                                  
> 
> Some notes on the way the fallback content is now rendered: 
> 
>     - The fallback content is rendered inside an inline-block so it does not calculate 
>       its dimensions the way a replaced element (i.e. an image) would (as defined by
>       http://www.w3.org/TR/CSS2/visudet.html#inline-replaced-width). So where one of width 
>       or height is auto but the other is not, the fallback content will not exactly match 
>       the dimensions calculated by RenderImage in error mode currently. We do a modest
>       imitation of the logic in quirks mode, but in strict mode it will behave exactly like an inline-block.
> 
>     - Where the image has no src attribute and no alt attribute RenderImage.cpp
>       still looks after the painting of the element - no fallback content is generated
>       and no broken image is displayed. This is consistent with existing behaviour.
> 
>     - The only image resource requests that still use the synchronous load path are
>       those where the item is cached (and didn't error out), where it's a data: source,
>       where its the fallback image for an object element, or where it's the image 
>       for a main resource load. All other image loads are now asynchronous so that
>       fallback content can be loaded outside the style recalc phase.
> 
> 
>     - Instead of aborting an image resource request when the src element is empty
>       (i.e. src='') we now allow the request to go through so that it can fail and
>       invoke the fallback content in HTMLImageLoader.cpp.   
> 
>     - As you can see in the new result for fast/borders/rtl-border-05.html, since
>       the alt-text is displayed as an inline-block it no longer artificially shrinks
>       any border on the element to the broken-image icon.   
> 
> Some notes on the rebaselined test results:                 
> 
>     - I've modified inspector/network/network-image-404.html to output the state of
>       both the resource requests, i.e. the failed one and the resource request for the
>       data:png to display the broken image icon.            
> 
>     - I've added a missing support file for fast/css/counters/complex-before.html -
>       its absence meant that the result was polluted by the behaviour of broken image
>       rendering.                                            
> 
>     - Likewise for fast/images/imagemap-polygon* tests - our new rendering of failed
>       image loads was interfering with an assumption in the tests that a broken image
>       still painted a RenderImage. So I've removed the src attribute to allow the
>       assumption hold (img elements without a src attribute are painted by
>       RenderImage).
> 
>     - http/tests/security/local-image-from-remote-whitelisted.html has been masking
>       a bug - blink does not load the image even though it is whitelisted. I am
>       rebaselining the test to reflect the failure revealed by this CL and tracking 
>       a fix under crbug.com/410949.                         
> 
>     - I have altered fast/forms/state-restore-to-non-edited-controls.html to wait 
>       100ms before submitting the form as the image load in the input element is now 
>       asynchronous.
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=184770

TBR=esprehn@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/696123002

git-svn-id: svn://svn.chromium.org/blink/trunk@184773 bbb929c8-8fbe-4397-9dbb-9b2b20218538