Fix incorrect implementation of NSTextInputClient.

content/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <Carbon/Carbon.h>
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
@@ skipping 2999 matching lines @@
 
   NSRect rect = [self firstViewRectForCharacterRange:theRange
                                          actualRange:actualRange];
 
   // Convert into screen coordinates for return.
   rect = [self convertRect:rect toView:nil];
   rect = [[self window] convertRectToScreen:rect];
   return rect;
 }
 
+- (NSRange)selectedRange {
+  if (selectedRange_.location == NSNotFound)
+    return NSMakeRange(NSNotFound, 0);
+  return selectedRange_;
+}
+
 - (NSRange)markedRange {
   // An input method calls this method to check if an application really has
   // a text being composed when hasMarkedText call returns true.
   // Returns the range saved in the setMarkedText method so the input method
   // calls the setMarkedText method and we can update the composition node
   // there. (When this method returns an empty range, the input method doesn't
   // call the setMarkedText method.)
   return hasMarkedText_ ? markedRange_ : NSMakeRange(NSNotFound, 0);
 }
 
 - (NSAttributedString*)attributedSubstringForProposedRange:(NSRange)range
     actualRange:(NSRangePointer)actualRange {
-  // TODO(thakis): Pipe |actualRange| through TextInputClientMac machinery.
+  // Prepare |actualRange| as if the proposed range is invalid. If it is valid,
+  // then |actualRange| will be updated again.
   if (actualRange)
-    *actualRange = range;
+    *actualRange = NSMakeRange(NSNotFound, 0);
+
+  // The caller of this method is allowed to pass nonsensical ranges. These
+  // can't even be converted into gfx::Ranges.
+  if (range.location == NSNotFound || range.length == 0)
+    return nil;
+  if (range.length >= std::numeric_limits<NSUInteger>::max() - range.location)
+    return nil;
 
   const gfx::Range requested_range(range);
   if (requested_range.is_reversed())
     return nil;
 
   gfx::Range expected_range;
   const base::string16* expected_text;
 
   if (!renderWidgetHostView_->composition_range().is_empty()) {
     expected_text = &markedText_;
     expected_range = renderWidgetHostView_->composition_range();
   } else {
     expected_text = &renderWidgetHostView_->selection_text();
     size_t offset = renderWidgetHostView_->selection_text_offset();
     expected_range = gfx::Range(offset, offset + expected_text->size());
   }
 
-  if (!expected_range.Contains(requested_range))
+  gfx::Range actual_range = expected_range.Intersect(requested_range);
+  if (!actual_range.IsValid())
     return nil;
 
   // Gets the raw bytes to avoid unnecessary string copies for generating
   // NSString.
   const base::char16* bytes =
-      &(*expected_text)[requested_range.start() - expected_range.start()];
+      &(*expected_text)[actual_range.start() - expected_range.start()];
   // Avoid integer overflow.
-  base::CheckedNumeric<size_t> requested_len = requested_range.length();
+  base::CheckedNumeric<size_t> requested_len = actual_range.length();
   requested_len *= sizeof(base::char16);
   NSUInteger bytes_len = base::strict_cast<NSUInteger, size_t>(
       requested_len.ValueOrDefault(0));
   base::scoped_nsobject<NSString> ns_string(
       [[NSString alloc] initWithBytes:bytes
                                length:bytes_len
                              encoding:NSUTF16LittleEndianStringEncoding]);
+  if (actualRange)
+    *actualRange = actual_range.ToNSRange();
+
   return [[[NSAttributedString alloc] initWithString:ns_string] autorelease];
 }
 
 - (NSInteger)conversationIdentifier {
   return reinterpret_cast<NSInteger>(self);
 }
 
 // Each RenderWidgetHostViewCocoa has its own input context, but we return
 // nil when the caret is in non-editable content or password box to avoid
 // making input methods do their work.
@@ skipping 342 matching lines @@
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end