Add testRunner callbacks for better handling of view-source frames

testRunner.setViewSorceForFrame() allows us test an interaction between the 
view-souce feature and the XSSAuditor in blink. The current technique for testing
view-source pages is to use a hack in the content_shell's dump-render-tree mode
to turn on view-source for the main page when the path /viewsource/ is 
present in the URL.

To test XSS reflections, however, there needs to be a query string containing
the reflection (because putting it in the path would lead to horribly named 
files). To get a query string, we traditionally load a main page which then
loads the more complex URL in a iframe.  Presently, there's no way to make
that iframe a view-source frame (since some guy removed the viewsource="true"
attribute from HTML because it was dangerous).

There are also two other methods that are exposed to javascript: dumpAsMarkup()
and dumpChildFramesAsMarkup().  These give the test scripts the ability to control
the format of the output.  This is needed to simplify diffing the results 
of these kinds of tests.

CL https://codereview.chromium.org/301813002/ is blocked on this.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=274304

[Tom Sepez, 2014-05-29 21:07:44]

+tkent for OWNERS review.

[tkent, 2014-05-30 00:52:47]

lgtm

[Tom Sepez, 2014-05-30 16:37:38]

@tkent - Sorry, I made a few more changes. Let me know if it's still OK.

[tkent, 2014-06-01 23:28:31]

lgtm.

I wonder if we need both of dumpAsMarkup and dumpChildFramesAsMarkup.  Can
dumpChildFramesAsMarkup cover all usecases?

[Tom Sepez, 2014-06-02 16:59:35]

The CQ bit was checked by tsepez@chromium.org

[commit-bot: I haz the power, 2014-06-02 17:00:04]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/tsepez@chromium.org/302043002/80001

[Tom Sepez, 2014-06-02 17:00:50]

> I wonder if we need both of dumpAsMarkup and dumpChildFramesAsMarkup.  Can
> dumpChildFramesAsMarkup cover all usecases?
I was thinking the same thing.  dumpChildFrames() should be sufficient, but
there's a lot of files to change.

[Tom Sepez, 2014-06-02 17:52:11]

> dumpChildFrames() should be sufficient, but there's a lot of files to change.
Filed https://code.google.com/p/chromium/issues/detail?id=379827 as followup.

[commit-bot: I haz the power, 2014-06-02 19:27:17]

Change committed as 274304