add customized printing setting for headless

third_party/WebKit/Source/core/inspector/browser_protocol.json

Index: third_party/WebKit/Source/core/inspector/browser_protocol.json
diff --git a/third_party/WebKit/Source/core/inspector/browser_protocol.json b/third_party/WebKit/Source/core/inspector/browser_protocol.json
index cca3bc914abf20def2b85f6c03a4bedc80a611dd..59e300656a8f5a002dc0a4333f0c20f837fc8672 100644
--- a/third_party/WebKit/Source/core/inspector/browser_protocol.json
+++ b/third_party/WebKit/Source/core/inspector/browser_protocol.json
@@ -430,6 +430,20 @@
             {
                 "name": "printToPDF",
                 "description": "Print page as pdf.",
+                "parameters": [
+                    {"name": "dpi", "type": "integer", "optional": true, "description": "DPI of the printed file."},

[Eric Seckler, 2017/04/20 09:15:28]

what's the default value? also, this doesn't seem to have any effect on MacOS
(should it?), maybe that justifies a comment here :)

[jzfeng, 2017/04/27 06:56:07]

Removed this parameter, because it is not well supported yet.

+                    {"name": "landscape", "type": "boolean", "optional": true, "description": "Paper orientation. Defaults to false."},
+                    {"name": "displayHeaderFooter", "type": "boolean", "optional": true, "description": "Display header and footer. Defaults to false."},
+                    {"name": "printBackgrounds", "type": "boolean", "optional": true, "description": "Print background graphics. Defaults to false."},

[Eric Seckler, 2017/04/20 09:15:28]

nit: colors/graphics

[jzfeng, 2017/04/27 06:56:07]

Done.

+                    {"name": "scale", "type": "number", "optional": true, "description": "Scale of the pdf. Defaults to 1."},
+                    {"name": "paperType", "type": "string", "optional": true, "enum": ["letter", "legal", "A4", "A3"], "description": "Paper type. Defaults to 'letter'."},

[Eric Seckler, 2017/04/20 09:15:28]

Are these all the paper sizes we can support? Maybe it'd be more useful to pass
the actual width/height (millimeters/inches) instead.

[Lei Zhang, 2017/04/20 19:08:59]

That's a product decision. If you go with only mm or inches, then some part of
the world is going to be slightly unhappy. e.g. A4 is some odd number of inches,
and ditto for Letter in mm.

[martinsb, 2017/04/26 08:10:00]

Thank you very much for your efforts, I have no doubt that PDF printing
customization is an essential and very welcome feature.
There may be multiple use cases when a custom size is required. We at infogr.am
(https://infogr.am) would be happy to migrate our document export to PDF from
PhantomJS to headless chromium, however not being able to specify custom size
for the output PDF (in inches, millimeters, microns or anything else) still
would be a deal breaker for us. 

[jzfeng, 2017/04/27 06:56:07]

Add a new "CUSTOM" page type to let the user specify page width and height. Also
add a "unit" parameter to the command to let the user specify using mm or inch.
Hence, user can pick popular page types, such as letter. They can also specify
an arbitrary page size as they wish.

[Eric Seckler, 2017/04/27 08:57:00]

For my taste, this is more complicated than it needs to be. I'd be happier if we
fixed this to one unit (inches, for argument's sake, since that's what the
printing system seems to use). Users can then look up and specify page sizes in
inches themselves. I don't think it's necessary for us to supply "common" page
sizes ourselves - that just opens us up to people asking for more explicitly
listed page sizes in the protocol. WDYT?

[jzfeng, 2017/05/02 07:50:55]

Sounds good. Done.

+                    {"name": "marginType", "type": "string", "optional": true, "enum": ["defaultMargin", "noMargin", "customMargin"], "description": "Margin type. Set to 'customMargin' to customize margin."},

[Eric Seckler, 2017/04/20 09:15:28]

I'm not sure we need this field. I'd propose we get rid of it and:
- by default, marginTop/Bottom/Left/Right is set to "defaultMargin" values.
- if the user doesn't want any margin, they can set marginTop/Bottom/Left/Right
to 0.
- if the user wants a custom margin, they can set marginTop/Bottom/Left/Right to
a custom value.

[jzfeng, 2017/04/27 06:56:07]

Sounds good. Done.

+                    {"name": "marginTop", "type": "number", "optional": true, "description": "Top margin in inch. Set when margin type is 'custom'."},
+                    {"name": "marginBottom", "type": "number", "optional": true, "description": "Bottom margin in inch. Set when margin type is 'custom'."},
+                    {"name": "marginLeft", "type": "number", "optional": true, "description": "Left margin in inch. Set when margin type is 'custom'."},
+                    {"name": "marginRight", "type": "number", "optional": true, "description": "Right margin in inch. Set when margin type is 'custom'."},
+                    {"name": "pageRanges", "type": "string", "optional": true, "description": "Paper ranges to print, e.g., '1-5, 8, 11-13'. Defaults to print all pages."}
+                ],
                 "returns": [
                     { "name": "data", "type": "string", "description": "Base64-encoded pdf data." }
                 ],