Debugger: Restrict LocationMark dragging

... to engines that actually support JumpToLine and make it
work in disassembler views.

Change-Id: I10368ea719587caa7c4f33665eff57c2bf300d84
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/sourceutils.h

@@ -33,12 +33,18 @@
 
 #include <QString>
 
-namespace TextEditor { class TextEditorWidget; }
+namespace TextEditor {
+class TextDocument;
+class TextEditorWidget;
+}
+
 namespace CPlusPlus { class Snapshot; }
 
 namespace Debugger {
 namespace Internal {
 
+class ContextData;
+
 // Editor tooltip support
 QString cppExpressionAt(TextEditor::TextEditorWidget *editorWidget, int pos,
                         int *line, int *column, QString *function = 0,
@@ -53,6 +59,8 @@ bool getUninitializedVariables(const CPlusPlus::Snapshot &snapshot,
    const QString &function, const QString &file, int line,
    QStringList *uninitializedVariables);
 
+ContextData getLocationContext(TextEditor::TextDocument *document, int lineNumber);
+
 } // namespace Internal
 } // namespace Debugger