Give loose contraints to text inside input widget

The input widget scrolls, so it should give its text loose constraints.  That
way the text ends up being its intrinsic size even if put in a context with
tight constraints.

Fixes #298

packages/flutter/lib/src/material/input.dart

@@ -167,7 +167,7 @@ class InputState extends ScrollableState<Input> {
     scrollTo(scrollBehavior.updateExtents(
       contentExtent: _contentWidth,
       containerExtent: _containerWidth,
-      scrollOffset: _contentWidth)
-    );
+      scrollOffset: _contentWidth
+    ));
   }
 }

packages/flutter/lib/src/painting/text_painter.dart

@@ -177,10 +177,18 @@ class TextPainter {
     return _applyFloatingPointHack(_paragraph.maxIntrinsicWidth);
   }
 
+  double get width {
+    assert(!_needsLayout);
+    return _applyFloatingPointHack(_paragraph.width);
+  }
+
+  double get height {
+    assert(!_needsLayout);
+    return _applyFloatingPointHack(_paragraph.height);
+  }
+
   Size get size {
     assert(!_needsLayout);
-    double height = _applyFloatingPointHack(_paragraph.height);
-    double width = _applyFloatingPointHack(_paragraph.width);
     return new Size(width, height);
   }
 

packages/flutter/lib/src/rendering/editable_paragraph.dart

@@ -60,15 +60,21 @@ class RenderEditableParagraph extends RenderParagraph {
     markNeedsPaint();
   }
 
-  // Editable text does not support line wrap.
-  bool get allowLineWrap => false;
+  BoxConstraints _getTextContraints(BoxConstraints constraints) {
+    return new BoxConstraints(
+      minWidth: 0.0,
+      maxWidth: double.INFINITY,
+      minHeight: constraints.minHeight,
+      maxHeight: constraints.maxHeight
+    );
+  }
 
   double _getIntrinsicWidth(BoxConstraints constraints) {
     // There should be no difference between the minimum and maximum width
     // because we only support single-line text.
-    layoutText(constraints);
+    layoutText(_getTextContraints(constraints));
     return constraints.constrainWidth(
-      textPainter.size.width + _kCursorGap + _kCursorWidth
+      textPainter.width + _kCursorGap + _kCursorWidth
     );
   }
 
@@ -81,23 +87,21 @@ class RenderEditableParagraph extends RenderParagraph {
   }
 
   void performLayout() {
-    layoutText(constraints);
+    layoutText(_getTextContraints(constraints));
+    Size contentSize = new Size(textPainter.width + _kCursorGap + _kCursorWidth, textPainter.height);
+    size = constraints.constrain(contentSize);
 
-    Offset cursorPadding = const Offset(_kCursorGap + _kCursorWidth, 0.0);
-    Size newContentSize = textPainter.size + cursorPadding;
-    size = constraints.constrain(newContentSize);
-
-    if (_contentSize == null || _contentSize != newContentSize) {
-      _contentSize = newContentSize;
+    if (_contentSize == null || _contentSize != contentSize) {
+      _contentSize = contentSize;
       if (onContentSizeChanged != null)
-        onContentSizeChanged(newContentSize);
+        onContentSizeChanged(_contentSize);
     }
   }
 
   void paint(PaintingContext context, Offset offset) {
-    layoutText(constraints);
+    layoutText(_getTextContraints(constraints));
 
-    bool needsClipping = (_contentSize.width > size.width);
+    final bool needsClipping = (_contentSize.width > size.width);
     if (needsClipping) {
       context.canvas.save();
       context.canvas.clipRect(offset & size);
@@ -107,15 +111,12 @@ class RenderEditableParagraph extends RenderParagraph {
 
     if (_showCursor) {
       Rect cursorRect =  new Rect.fromLTWH(
-        textPainter.size.width + _kCursorGap,
-        _kCursorHeightOffset,
+        offset.dx + _contentSize.width - _kCursorWidth - _scrollOffset.dx,
+        offset.dy + _kCursorHeightOffset - _scrollOffset.dy,
         _kCursorWidth,
         size.height - 2.0 * _kCursorHeightOffset
       );
-      context.canvas.drawRect(
-        cursorRect.shift(offset - _scrollOffset),
-        new Paint()..color = _cursorColor
-      );
+      context.canvas.drawRect(cursorRect, new Paint()..color = _cursorColor);
     }
 
     if (needsClipping)

packages/flutter/lib/src/rendering/paragraph.dart

@@ -47,14 +47,11 @@ class RenderParagraph extends RenderBox {
     markNeedsLayout();
   }
 
-  // Whether the text should be allowed to wrap to multiple lines.
-  bool get allowLineWrap => true;
-
   void layoutText(BoxConstraints constraints) {
     assert(constraints != null);
     if (_constraintsForCurrentLayout == constraints)
       return; // already cached this layout
-    textPainter.maxWidth = allowLineWrap ? constraints.maxWidth : double.INFINITY;
+    textPainter.maxWidth = constraints.maxWidth;
     textPainter.minWidth = constraints.minWidth;
     textPainter.minHeight = constraints.minHeight;
     textPainter.maxHeight = constraints.maxHeight;