Implement Views framework on Windows and Linux (issue #1749).

- Add Views header files in a new include/views directory.
- Add initial top-level window (CefWindow), control (CefBrowserView,
  CefLabelButton, CefMenuButton, CefPanel, CefScrollView,
  CefTextfield) and layout (CefBoxLayout, CefFlowLayout) support.
  See libcef/browser/views/view_impl.h comments for implementation
  details.
- Add Views example usage in cefclient and cefsimple and Views unit
  tests in cef_unittests. Pass the `--use-views` command-line flag to
  cefclient, cefsimple and cef_unittests to run using the Views
  framework instead of platform APIs. For cefclient and cefsimple
  this will create the browser window and all related functionality
  using the Views framework. For cef_unittests this will run all
  tests (except OSR tests) in a Views-based browser window. Views-
  specific unit tests (`--gtest_filter=Views*`) will be run even if
  the the `--use-views` flag is not specified.
- Pass the `--hide-frame` command-line flag to cefclient to demo a
  frameless Views-based browser window.
- Pass the `--hide-controls` command-line flag to cefclient to demo a
  browser window without top controls. This also works in non-Views
  mode.
- Pass the `--enable-high-dpi-support` command-line flag to
  cef_unittests on Windows to test high-DPI support on a display
  that supports it.
- Add CefImage for reading/writing image file formats.
- Add CefBrowser::DownloadImage() for downloading image URLs as a
  CefImage representation. This is primarily for loading favicons.
- Add CefMenuModel::CreateMenuModel() and CefMenuModelDelegate for
  creating custom menus. This is primarily for use with
  CefMenuButton.
- Add CefBrowser::TryCloseBrowser() helper for closing a browser.
  Also improve related documentation in cef_life_span_handler.h.
- Rename cef_page_range_t to cef_range_t. It is now also used by
  CefTextfield.
- Remove CefLifeSpanHandler::RunModal() which is never called.
- Add draggable regions example to cefclient.

include/capi/cef_browser_capi.h

@@ -41,6 +41,7 @@
 #include "include/capi/cef_base_capi.h"
 #include "include/capi/cef_drag_data_capi.h"
 #include "include/capi/cef_frame_capi.h"
+#include "include/capi/cef_image_capi.h"
 #include "include/capi/cef_navigation_entry_capi.h"
 #include "include/capi/cef_process_message_capi.h"
 #include "include/capi/cef_request_context_capi.h"
@@ -251,6 +252,29 @@ typedef struct _cef_pdf_print_callback_t {
 } cef_pdf_print_callback_t;
 
 
+///
+// Callback structure for cef_browser_host_t::DownloadImage. The functions of
+// this structure will be called on the browser process UI thread.
+///
+typedef struct _cef_download_image_callback_t {
+  ///
+  // Base structure.
+  ///
+  cef_base_t base;
+
+  ///
+  // Method that will be executed when the image download has completed.
+  // |image_url| is the URL that was downloaded and |http_status_code| is the
+  // resulting HTTP status code. |image| is the resulting image, possibly at
+  // multiple scale factors, or NULL if the download failed.
+  ///
+  void (CEF_CALLBACK *on_download_image_finished)(
+      struct _cef_download_image_callback_t* self,
+      const cef_string_t* image_url, int http_status_code,
+      struct _cef_image_t* image);
+} cef_download_image_callback_t;
+
+
 ///
 // Structure used to represent the browser process aspects of a browser window.
 // The functions of this structure can only be called in the browser process.
@@ -282,6 +306,16 @@ typedef struct _cef_browser_host_t {
   void (CEF_CALLBACK *close_browser)(struct _cef_browser_host_t* self,
       int force_close);
 
+  ///
+  // Helper for closing a browser. Call this function from the top-level window
+  // close handler. Internally this calls CloseBrowser(false (0)) if the close
+  // has not yet been initiated. This function returns false (0) while the close
+  // is pending and true (1) after the close has completed. See close_browser()
+  // and cef_life_span_handler_t::do_close() documentation for additional usage
+  // information. This function must be called on the browser process UI thread.
+  ///
+  int (CEF_CALLBACK *try_close_browser)(struct _cef_browser_host_t* self);
+
   ///
   // Set whether the browser is focused.
   ///
@@ -295,19 +329,27 @@ typedef struct _cef_browser_host_t {
       int visible);
 
   ///
-  // Retrieve the window handle for this browser.
+  // Retrieve the window handle for this browser. If this browser is wrapped in
+  // a cef_browser_view_t this function should be called on the browser process
+  // UI thread and it will return the handle for the top-level native window.
   ///
   cef_window_handle_t (CEF_CALLBACK *get_window_handle)(
       struct _cef_browser_host_t* self);
 
   ///
   // Retrieve the window handle of the browser that opened this browser. Will
-  // return NULL for non-popup windows. This function can be used in combination
-  // with custom handling of modal windows.
+  // return NULL for non-popup windows or if this browser is wrapped in a
+  // cef_browser_view_t. This function can be used in combination with custom
+  // handling of modal windows.
   ///
   cef_window_handle_t (CEF_CALLBACK *get_opener_window_handle)(
       struct _cef_browser_host_t* self);
 
+  ///
+  // Returns true (1) if this browser is wrapped in a cef_browser_view_t.
+  ///
+  int (CEF_CALLBACK *has_view)(struct _cef_browser_host_t* self);
+
   ///
   // Returns the client for this browser.
   ///
@@ -362,6 +404,22 @@ typedef struct _cef_browser_host_t {
   void (CEF_CALLBACK *start_download)(struct _cef_browser_host_t* self,
       const cef_string_t* url);
 
+  ///
+  // Download |image_url| and execute |callback| on completion with the images
+  // received from the renderer. If |is_favicon| is true (1) then cookies are
+  // not sent and not accepted during download. Images with density independent
+  // pixel (DIP) sizes larger than |max_image_size| are filtered out from the
+  // image results. Versions of the image at different scale factors may be
+  // downloaded up to the maximum scale factor supported by the system. If there
+  // are no image results <= |max_image_size| then the smallest image is resized
+  // to |max_image_size| and is the only result. A |max_image_size| of 0 means
+  // unlimited. If |bypass_cache| is true (1) then |image_url| is requested from
+  // the server even if it is present in the browser cache.
+  ///
+  void (CEF_CALLBACK *download_image)(struct _cef_browser_host_t* self,
+      const cef_string_t* image_url, int is_favicon, uint32 max_image_size,
+      int bypass_cache, struct _cef_download_image_callback_t* callback);
+
   ///
   // Print the current browser contents.
   ///
@@ -398,7 +456,9 @@ typedef struct _cef_browser_host_t {
 
   ///
   // Open developer tools in its own window. If |inspect_element_at| is non-
-  // NULL the element at the specified (x,y) location will be inspected.
+  // NULL the element at the specified (x,y) location will be inspected. The
+  // |windowInfo| parameter will be ignored if this browser is wrapped in a
+  // cef_browser_view_t.
   ///
   void (CEF_CALLBACK *show_dev_tools)(struct _cef_browser_host_t* self,
       const struct _cef_window_info_t* windowInfo,