Updating screenshot code to prevent resizing if window is large enough.

In the previous screenshot update, the driver would incorrectly resize
the IE window smaller if the document was smaller in height or width
than the current window size. This could cause redraws of the page
being viewed such that after resizing, the screenshot still did not
display the entire page. This commit resolves that issue, and also takes
into account the size of the scroll bars when creating the screenshot
image. NOTE: There is a *very* slight chance that resizing the window
so there are no longer scroll bars to be displayed *might* still cause
layout redraws such that the screenshot does not show the entire DOM
after the resize. Since we should now always be expanding the window size,
never contracting it, this is a corner case that explicitly will *not* be
fixed. Any issue reports describing this corner case will be closed
without action. Fixes issue SeleniumHQ#1085.

cpp/iedriver/CommandHandlers/ScreenshotCommandHandler.h

@@ -132,8 +132,8 @@ class ScreenshotCommandHandler : public IECommandHandler {
     int target_window_height = document_info.height + chrome_height;
 
     // For some reason, this technique does not allow the user to resize
-    // the browser window to greater than SIZE_LIMIT x SIZE_LIMIT. This is pretty
-    // big, so we'll cap the allowable screenshot size to that.
+    // the browser window to greater than SIZE_LIMIT x SIZE_LIMIT. This is
+    // pretty big, so we'll cap the allowable screenshot size to that.
     //
     // GDI+ limit after which it may report Generic error for some image types
     int SIZE_LIMIT = 65534; 
@@ -153,6 +153,30 @@ class ScreenshotCommandHandler : public IECommandHandler {
     LOG(DEBUG) << "Initial browser window sizes are (w, h): "
                << original_width << ", " << original_height;
 
+    // If the window is already wide enough to accomodate
+    // the document, don't resize that dimension. Otherwise,
+    // the window will display a horizontal scroll bar, and
+    // we need to take the scroll bar height into account when
+    // we size resulting image.
+    int horizontal_scrollbar_height = 0;
+    if (original_width > target_window_width) {
+      target_window_width = original_width;
+    } else {
+      horizontal_scrollbar_height = ::GetSystemMetrics(SM_CYHSCROLL);
+    }
+
+    // If the window is already tall enough to accomodate
+    // the document, don't resize that dimension. Otherwise,
+    // the window will display a vertical scroll bar, and
+    // we need to take the scrollbar width into account when
+    // we size the resulting image.
+    int vertical_scrollbar_width = 0;
+    if (original_height > target_window_height) {
+      target_window_height = original_height;
+    } else {
+      vertical_scrollbar_width = ::GetSystemMetrics(SM_CXVSCROLL);
+    }
+
     BOOL is_maximized = ::IsZoomed(ie_window_handle);
     bool requires_resize = original_width < target_window_width ||
                            original_height < target_window_height;
@@ -168,6 +192,13 @@ class ScreenshotCommandHandler : public IECommandHandler {
         ::ShowWindow(ie_window_handle, SW_SHOWNORMAL);
       }
 
+      // NOTE: There is a *very* slight chance that resizing the window
+      // so there are no longer scroll bars to be displayed *might* cause
+      // layout redraws such that the screenshot does not show the entire
+      // DOM after the resize. Since we should always be expanding the
+      // window size, never contracting it, this is a corner case that
+      // explicitly will *not* be fixed. Any issue reports describing this
+      // corner case will be closed without action.
       RECT ie_window_rect;
       ::GetWindowRect(ie_window_handle, &ie_window_rect);
       ::SetWindowPos(ie_window_handle,
@@ -180,9 +211,10 @@ class ScreenshotCommandHandler : public IECommandHandler {
     }
 
     // Capture the window's canvas to a DIB.
-    BOOL created = this->image_->Create(document_info.width,
-                                        document_info.height,
-                                        /*numbers of bits per pixel = */ 32);
+    BOOL created = this->image_->Create(
+        document_info.width + vertical_scrollbar_width,
+        document_info.height + horizontal_scrollbar_height,
+        /*numbers of bits per pixel = */ 32);
     if (!created) {
       LOG(WARN) << "Unable to initialize image object";
     }