Change all platforms except Windows to access the clipboard solely from the UI thread

ui/base/clipboard/clipboard_mac.mm

Index: ui/base/clipboard/clipboard_mac.mm
diff --git a/ui/base/clipboard/clipboard_mac.mm b/ui/base/clipboard/clipboard_mac.mm
index 0398ce0d359a1f27147939a29e13e40801165624..2aecaccf8bc4ada6cb49fd734df0fb44d0258da4 100644
--- a/ui/base/clipboard/clipboard_mac.mm
+++ b/ui/base/clipboard/clipboard_mac.mm
@@ -79,12 +79,15 @@ Clipboard::FormatType Clipboard::FormatType::Deserialize(
 }
 
 Clipboard::Clipboard() {
+  DCHECK(CalledOnValidThread());
 }
 
 Clipboard::~Clipboard() {
+  DCHECK(CalledOnValidThread());
 }
 
 void Clipboard::WriteObjects(Buffer buffer, const ObjectMap& objects) {
+  DCHECK(CalledOnValidThread());
   DCHECK_EQ(buffer, BUFFER_STANDARD);
 
   NSPasteboard* pb = GetPasteboard();
@@ -211,6 +214,7 @@ void Clipboard::WriteWebSmartPaste() {
 }
 
 uint64 Clipboard::GetSequenceNumber(Buffer buffer) {
+  DCHECK(CalledOnValidThread());
   DCHECK_EQ(buffer, BUFFER_STANDARD);
 
   NSPasteboard* pb = GetPasteboard();
@@ -219,6 +223,7 @@ uint64 Clipboard::GetSequenceNumber(Buffer buffer) {
 
 bool Clipboard::IsFormatAvailable(const FormatType& format,
                                   Buffer buffer) const {
+  DCHECK(CalledOnValidThread());
   DCHECK_EQ(buffer, BUFFER_STANDARD);
 
   NSPasteboard* pb = GetPasteboard();
@@ -236,6 +241,7 @@ bool Clipboard::IsFormatAvailable(const FormatType& format,
 void Clipboard::ReadAvailableTypes(Clipboard::Buffer buffer,
                                    std::vector<string16>* types,
                                    bool* contains_filenames) const {
+  DCHECK(CalledOnValidThread());
   types->clear();
   if (IsFormatAvailable(Clipboard::GetPlainTextFormatType(), buffer))
     types->push_back(UTF8ToUTF16(kMimeTypeText));
@@ -254,6 +260,7 @@ void Clipboard::ReadAvailableTypes(Clipboard::Buffer buffer,
 }
 
 void Clipboard::ReadText(Clipboard::Buffer buffer, string16* result) const {
+  DCHECK(CalledOnValidThread());
   DCHECK_EQ(buffer, BUFFER_STANDARD);
   NSPasteboard* pb = GetPasteboard();
   NSString* contents = [pb stringForType:NSStringPboardType];
@@ -265,6 +272,7 @@ void Clipboard::ReadText(Clipboard::Buffer buffer, string16* result) const {
 
 void Clipboard::ReadAsciiText(Clipboard::Buffer buffer,
                               std::string* result) const {
+  DCHECK(CalledOnValidThread());
   DCHECK_EQ(buffer, BUFFER_STANDARD);
   NSPasteboard* pb = GetPasteboard();
   NSString* contents = [pb stringForType:NSStringPboardType];
@@ -278,6 +286,7 @@ void Clipboard::ReadAsciiText(Clipboard::Buffer buffer,
 void Clipboard::ReadHTML(Clipboard::Buffer buffer, string16* markup,
                          std::string* src_url, uint32* fragment_start,
                          uint32* fragment_end) const {
+  DCHECK(CalledOnValidThread());
   DCHECK_EQ(buffer, BUFFER_STANDARD);
 
   // TODO(avi): src_url?
@@ -306,6 +315,7 @@ void Clipboard::ReadHTML(Clipboard::Buffer buffer, string16* markup,
 }
 
 SkBitmap Clipboard::ReadImage(Buffer buffer) const {
+  DCHECK(CalledOnValidThread());
   DCHECK_EQ(buffer, BUFFER_STANDARD);
 
   scoped_nsobject<NSImage> image(
@@ -336,6 +346,7 @@ SkBitmap Clipboard::ReadImage(Buffer buffer) const {
 void Clipboard::ReadCustomData(Buffer buffer,
                                const string16& type,
                                string16* result) const {
+  DCHECK(CalledOnValidThread());
   DCHECK_EQ(buffer, BUFFER_STANDARD);
 
   NSPasteboard* pb = GetPasteboard();
@@ -347,6 +358,7 @@ void Clipboard::ReadCustomData(Buffer buffer,
 }
 
 void Clipboard::ReadBookmark(string16* title, std::string* url) const {
+  DCHECK(CalledOnValidThread());
   NSPasteboard* pb = GetPasteboard();
 
   if (title) {
@@ -366,6 +378,7 @@ void Clipboard::ReadBookmark(string16* title, std::string* url) const {
 }
 
 void Clipboard::ReadData(const FormatType& format, std::string* result) const {
+  DCHECK(CalledOnValidThread());
   NSPasteboard* pb = GetPasteboard();
   NSData* data = [pb dataForType:format.ToNSString()];
   if ([data length])