Revert 163034 "Moved remaining legacy viewport tests to unit tests."

This caused Android Tests (dbg) to fail:
http://build.chromium.org/p/chromium.webkit/builders/Android%20Tests%20%28dbg%29/builds/15479

> Moved remaining legacy viewport tests to unit tests.
> 
> In https://codereview.chromium.org/48613005/ most of the legacy viewport
> meta tag tests were converted into unit tests. This CL moves the
> remaining "trickier" tests.
> 
> BUG=314001
> 
> Review URL: https://codereview.chromium.org/99223005

TBR=bokan@chromium.org

Review URL: https://codereview.chromium.org/101693002

git-svn-id: svn://svn.chromium.org/blink/trunk@163077 bbb929c8-8fbe-4397-9dbb-9b2b20218538
This code originally use specialised templates for "switching on type". This change instead uses run time switching to try and make the code more readable.

BUG=

Review URL: https://codereview.chromium.org/63913003

git-svn-id: svn://svn.chromium.org/blink/trunk@163078 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Added setters and getters in WebLayer.h / GraphicsLayer.h for:
* blendMode - specifying the formula for blending the layer with its backdrop - http://dev.w3.org/fxtf/compositing-1/#blending
* isIsolatedGroupRoot - this layer should make sure that all its blending child layers in the layer tree and the layer itself will use a transparent black initial backdrop. http://dev.w3.org/fxtf/compositing-1/#isolatedgroups

Added WebBlendMode.h defining the WebBlendMode enum and convertion functions.

Added a new compositing reason - CompositingReasonIsolateCompositedDescendants. A RenderLayer might require compositing in order to perform isolation of its composited blending children

BUG=243223

Review URL: https://codereview.chromium.org/23511004

git-svn-id: svn://svn.chromium.org/blink/trunk@163079 bbb929c8-8fbe-4397-9dbb-9b2b20218538