Add support for style="page-break-inside:avoid" to wxHTML

Allow using this style to prevent page breaks inside the given <div>.

tests/html/htmprint.cpp

@@ -107,6 +107,74 @@ TEST_CASE("wxHtmlPrintout::Pagination", "[html][print]")
             "</div>"
        );
     CHECK( CountPages(pr) == 2 );
+
+    // Also test that forbidding page breaks inside a paragraph works: it
+    // should move it entirely to the next page, resulting in one extra page
+    // compared to the version without "page-break-inside: avoid".
+    static const char* const text =
+"Early in the morning on the fourteenth of the spring month of Nisan the "
+"Procurator of Judea, Pontius Pilate, in a white cloak lined with blood red, "
+"emerged with his shuffling cavalryman's walk into the arcade connecting the two "
+"wings of the palace of Herod the Great. "
+"\n"
+"More than anything else in the world the Procurator hated the smell of attar of "
+"roses.  The omens for the day were bad, as this scent had been haunting him "
+"since dawn. "
+"\n"
+"It seemed to the Procurator that the very cypresses and palms in the garden "
+"were exuding the smell of roses, that this damned stench of roses was even "
+"mingling with the smell of leather tackle and sweat from his mounted bodyguard. "
+"\n"
+"A haze of smoke was drifting toward the arcade across the upper courtyard of "
+"the garden, coming from the wing at the rear of the palace, the quarters of the "
+"first cohort of the XII Legion; known as the \"Lightning,\" it had been "
+"stationed in Jerusalem since the Procurator's arrival.  The same oily perfume "
+"of roses was mixed with the acrid smoke that showed that the centuries' cooks "
+"had started to prepare breakfast "
+"\n"
+"\"Oh, gods, what are you punishing me for?..  No, there's no doubt, I have it "
+"again, this terrible incurable pain...  hemicrania, when half the head aches... "
+"There's no cure for it, nothing helps...  I must try not to move my head...\" "
+"\n"
+"A chair had already been placed on the mosaic floor by the fountain; without a "
+"glance around, the Procurator sat in it and stretched out his hand to one side. "
+"His secretary deferentially laid a piece of parchment in his hand.  Unable to "
+"restrain a grimace of agony, the Procurator gave a fleeting sideways look at "
+"its contents, returned the parchment to his secretary and said painfully, \"The "
+"accused comes from Galilee, does he?  Was the case sent to the tetrarch?\" "
+"\n"
+"\"Yes, Procurator,\" replied the secretary.  \"He declined to confirm the "
+"finding of the court and passed the Sanhedrin's sentence of death to you for "
+"confirmation.\" "
+"\n"
+"The Procurator's cheek twitched, and he said quietly, \"Bring in the accused.\" "
+        ;
+
+    pr.SetHtmlText
+       (
+            wxString::Format
+            (
+                "<img width=\"100\" height=\"600\" src=\"dummy\"/>"
+                "<div>%s</div>"
+                "<br/>"
+                "<img width=\"100\" height=\"600\" src=\"dummy\"/>",
+                text
+            )
+       );
+    CHECK( CountPages(pr) == 2 );
+
+    pr.SetHtmlText
+       (
+            wxString::Format
+            (
+                "<img width=\"100\" height=\"600\" src=\"dummy\"/>"
+                "<div style=\"page-break-inside:avoid\">%s</div>"
+                "<br/>"
+                "<img width=\"100\" height=\"600\" src=\"dummy\"/>",
+                text
+            )
+       );
+    CHECK( CountPages(pr) == 3 );
 }
 
 #endif //wxUSE_HTML