Breakout from  http://crbug.com/598051  --

svg/zoom/page/zoom-foreignObject.svg

Notes on zoom-foreignObject.svg --

Commenting out the second text block (svg foreign object) to focus on the html foreign object, the visual rect for the first line of text remains same from (A) initial frame to (B) the zoomed frame:

(A) 17:25:05.647 4920   {index: 4, client: "0x330c39668010 InlineTextBox 'This is a text'", type: "DrawingPaintPhaseForeground", rect: [0.000000,0.000000 75.000000x19.000000], cacheIsValid: true, visualRect: [0,0 230x78]},
(B) 17:25:05.648 4920   {index: 5, client: "0x330c39668010 InlineTextBox 'This is a text'", type: "DrawingPaintPhaseForeground", rect: [0.000000,0.000000 75.000000x19.000000], cacheIsValid: true, visualRect: [0,0 230x78]},

whereas most all other display items see their cull rect/visual rect grow for example:

(A) 17:25:05.647 4920   {index: 5, client: "0x330c39668088 InlineTextBox 'and a link.'", type: "DrawingPaintPhaseForeground", rect: [0.000000,20.000000 62.000000x19.000000], cacheIsValid: true, visualRect: [5,60 192x75]},
(B) 17:25:05.648 4920   {index: 6, client: "0x330c39668088 InlineTextBox 'and a link.'", type: "DrawingPaintPhaseForeground", rect: [0.000000,20.000000 62.000000x19.000000], cacheIsValid: true, visualRect: [7,87 276x107]},

It's particularly surprising since the '[HTML]' text in the test is:

  <xhtml:div>[HTML]</xhtml:div>

just like the one with the seemingly illegitimate visual rect two lines of code prior:

  <xhtml:div>This is a text</xhtml:div>

and yet:

(A) 17:35:15.446 1538   {index: 7, client: "0x12e848464178 InlineTextBox '[HTML]'", type: "DrawingPaintPhaseForeground", rect: [0.000000,40.000000 53.000000x19.000000], cacheIsValid: true, visualRect: [10,120 165x73]},
(B) 17:35:15.448 1538   {index: 8, client: "0x12e848464178 InlineTextBox '[HTML]'", type: "DrawingPaintPhaseForeground", rect: [0.000000,40.000000 53.000000x19.000000], cacheIsValid: true, visualRect: [15,174 237x103]},

I also wonder whether the cull rect is supposed to be growing in tandem with the visual rect. To investigate further.