Hopefully work around an MD downloads crash by suppressing zero-size drag components.

Chrome is experiencing crashes like this when a download is dragged:

> [Uncaught NSException] CALayerInvalidGeometry reason CALayer position
> contains NaN: [nan nan]

They started when I touched the dragging code at r545861 and, based on
some research, the probable cause is a zero-size component. I haven't
been able to trigger this locally so I'm guarding both of them.

Bug: 826632
Change-Id: I0e7c7acdd5a84dca8f0771aafab58987553b10e9
Reviewed-on: https://chromium-review.googlesource.com/1008502Reviewed-by: Leonard Grey <lgrey@chromium.org>
Commit-Queue: Sidney San Martín <sdy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549973}

chrome/browser/ui/cocoa/download/md_download_item_view.mm

@@ -648,24 +648,36 @@ NSTextField* MakeLabel(
                                                        downloadPath_.value())]]
       autorelease];
   draggingItem.imageComponentsProvider = ^{
-    NSDraggingImageComponent* imageComponent =
-        [[[NSDraggingImageComponent alloc]
-            initWithKey:NSDraggingImageComponentIconKey] autorelease];
-    NSImage* image = imageView_.image;
-    imageComponent.contents = image;
-    imageComponent.frame = imageRect;
-    NSDraggingImageComponent* labelComponent =
-        [[[NSDraggingImageComponent alloc]
-            initWithKey:NSDraggingImageComponentLabelKey] autorelease];
-
-    labelComponent.contents = [NSImage imageWithSize:labelRect.size
-                                             flipped:NO
-                                      drawingHandler:^(NSRect rect) {
-                                        [filename drawAtPoint:NSZeroPoint];
-                                        return YES;
-                                      }];
-    labelComponent.frame = labelRect;
-    return @[ imageComponent, labelComponent ];
+    // If either component is zero sized (which shouldn't generally happen, but
+    // apparently can… maybe a missing icon or empty string title?), omit it,
+    // else the dragging session will create layers with NaN components and
+    // crash.
+    auto* components = [NSMutableArray<NSDraggingImageComponent*> array];
+    if (imageRect.size.width != 0 && imageRect.size.height != 0) {
+      NSDraggingImageComponent* imageComponent =
+          [[[NSDraggingImageComponent alloc]
+              initWithKey:NSDraggingImageComponentIconKey] autorelease];
+      NSImage* image = imageView_.image;
+      imageComponent.contents = image;
+      imageComponent.frame = imageRect;
+      [components addObject:imageComponent];
+    }
+    if (labelRect.size.width != 0 && labelRect.size.height != 0) {
+      NSDraggingImageComponent* labelComponent =
+          [[[NSDraggingImageComponent alloc]
+              initWithKey:NSDraggingImageComponentLabelKey] autorelease];
+
+      labelComponent.contents = [NSImage imageWithSize:labelRect.size
+                                               flipped:NO
+                                        drawingHandler:^(NSRect rect) {
+                                          [filename drawAtPoint:NSZeroPoint];
+                                          return YES;
+                                        }];
+      labelComponent.frame = labelRect;
+      [components addObject:labelComponent];
+    }
+
+    return components;
   };
   [self beginDraggingSessionWithItems:@[ draggingItem ]
                                 event:event