Add :debug-dump-page command.

This can probably be merged into :download later, when the mess is cleaned up.

doc/help/commands.asciidoc

@@ -1226,6 +1226,7 @@ These commands are mainly intended for debugging. They are hidden if qutebrowser
 |<<debug-cache-stats,debug-cache-stats>>|Print LRU cache stats.
 |<<debug-console,debug-console>>|Show the debugging console.
 |<<debug-crash,debug-crash>>|Crash for debugging purposes.
+|<<debug-dump-page,debug-dump-page>>|Dump the current page's content to a file.
 |<<debug-pyeval,debug-pyeval>>|Evaluate a python string and display the results as a web page.
 |<<debug-trace,debug-trace>>|Trace executed code via hunter.
 |<<debug-webaction,debug-webaction>>|Execute a webaction.
@@ -1251,6 +1252,18 @@ Crash for debugging purposes.
 ==== positional arguments
 * +'typ'+: either 'exception' or 'segfault'.
 
+[[debug-dump-page]]
+=== debug-dump-page
+Syntax: +:debug-dump-page [*--plain*] 'dest'+
+
+Dump the current page's content to a file.
+
+==== positional arguments
+* +'dest'+: Where to write the file to.
+
+==== optional arguments
+* +*-p*+, +*--plain*+: Write plain text instead of HTML.
+
 [[debug-pyeval]]
 === debug-pyeval
 Syntax: +:debug-pyeval 's'+

qutebrowser/browser/commands.py

@@ -1225,6 +1225,24 @@ class CommandDispatcher:
         tab.setHtml(highlighted, current_url)
         tab.viewing_source = True
 
+    @cmdutils.register(instance='command-dispatcher', scope='window',
+                       debug=True)
+    def debug_dump_page(self, dest, plain=False):
+        """Dump the current page's content to a file.
+
+        Args:
+            dest: Where to write the file to.
+            plain: Write plain text instead of HTML.
+        """
+        web_view = self._current_widget()
+        mainframe = web_view.page().mainFrame()
+        if plain:
+            data = mainframe.toPlainText()
+        else:
+            data = mainframe.toHtml()
+        with open(dest, 'w', encoding='utf-8') as f:
+            f.write(data)
+
     @cmdutils.register(instance='command-dispatcher', name='help',
                        completion=[usertypes.Completion.helptopic],
                        scope='window')