Fix content.cache.size overflow with QtWebEngine

While 64-bit values are allowed with QtWebKit/QNetworkDiskCache, QtWebEngine
only allows 32-bit values here. With the updated sip's strict overflow checking,
that means we get an exception when setting a too big value.

doc/help/settings.asciidoc

@@ -1455,6 +1455,7 @@ This setting is only available with the QtWebKit backend.
 [[content.cache.size]]
 === content.cache.size
 Size (in bytes) of the HTTP network cache. Null to use the default value.
+With QtWebEngine, the maximum supported value is 2147483647 (~2 GB).
 
 Type: <<types,Int>>
 

qutebrowser/browser/webengine/webenginesettings.py

@@ -94,9 +94,10 @@ class DefaultProfileSetter(websettings.Base):
 
     """A setting set on the QWebEngineProfile."""
 
-    def __init__(self, setter, default=websettings.UNSET):
+    def __init__(self, setter, converter=None, default=websettings.UNSET):
         super().__init__(default)
         self._setter = setter
+        self._converter = converter
 
     def __repr__(self):
         return utils.get_repr(self, setter=self._setter, constructor=True)
@@ -105,7 +106,11 @@ class DefaultProfileSetter(websettings.Base):
         if settings is not None:
             raise ValueError("'settings' may not be set with "
                              "DefaultProfileSetters!")
+
         setter = getattr(default_profile, self._setter)
+        if self._converter is not None:
+            value = self._converter(value)
+
         setter(value)
 
 
@@ -296,7 +301,9 @@ MAPPINGS = {
         Attribute(QWebEngineSettings.LocalStorageEnabled),
     'content.cache.size':
         # 0: automatically managed by QtWebEngine
-        DefaultProfileSetter('setHttpCacheMaximumSize', default=0),
+        DefaultProfileSetter('setHttpCacheMaximumSize', default=0,
+                             converter=lambda val:
+                             qtutils.check_overflow(val, 'int', fatal=False)),
     'content.xss_auditing':
         Attribute(QWebEngineSettings.XSSAuditingEnabled),
     'content.default_encoding':

qutebrowser/config/configdata.yml

@@ -195,8 +195,10 @@ content.cache.size:
     none_ok: true
     minval: 0
     maxval: maxint64
-  desc: Size (in bytes) of the HTTP network cache. Null to use the default
-    value.
+  desc: >-
+    Size (in bytes) of the HTTP network cache. Null to use the default value.
+
+    With QtWebEngine, the maximum supported value is 2147483647 (~2 GB).
 
 # Defaults from QWebSettings::QWebSettings() in
 # qtwebkit/Source/WebKit/qt/Api/qwebsettings.cpp