Plumb physical backing size from RWHV to renderer CC.

This patch introduces a concept of "physical backing size" which is plumbed
down from port-specific browser code to the renderer compositor.

This is distinct from the usual concept of view size on high-DPI screens
with >1 dpi scale.  Physical backing size represents the size of the
texture CC draws to, whereas the view size is given to WebKit and
specifies the CSS width/height.

Before this patch, physical backing size was recalculated in the
renderer by multiplying the view size by DPI scale.  There are two problems
with this:

- This introduces off-by-one errors when DPI scale is non-integral.
  Values such as 1.5 and 1.33125 are common on Android devices.
- The Android port would like to more efficiently implement features like
  on-screen-keyboard bringup and URL-bar hiding without needing to
  resize the backing texture. Separating the value given to CC and to
  WebKit is the first step towards this.

WebKit counterpart at https://bugs.webkit.org/show_bug.cgi?id=110727

NOTRY=true
BUG=152502

Review URL: https://chromiumcodereview.appspot.com/12328080

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@185621 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 17 insertions, 1 deletions

diff --git a/content/browser/renderer_host/render_widget_host_view_base.cc b/content/browser/renderer_host/render_widget_host_view_base.cc
index a2cb5a4..f56413e 100644
--- a/content/browser/renderer_host/render_widget_host_view_base.cc
+++ b/content/browser/renderer_host/render_widget_host_view_base.cc
@@ -12,6 +12,8 @@
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebScreenInfo.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/screen.h"
+#include "ui/gfx/size_conversions.h"
+#include "ui/gfx/size_f.h"
 
 #if defined(OS_WIN)
 #include "base/command_line.h"
@@ -365,6 +367,14 @@ const SkBitmap& RenderWidgetHostViewBase::GetBackground() {
   return background_;
 }
 
+gfx::Size RenderWidgetHostViewBase::GetPhysicalBackingSize() const {
+  gfx::Display display =
+      gfx::Screen::GetNativeScreen()->GetDisplayNearestPoint(
+          GetViewBounds().origin());
+  return gfx::ToCeiledSize(gfx::ScaleSize(GetViewBounds().size(),
+                                          display.device_scale_factor()));
+}
+
 void RenderWidgetHostViewBase::SelectionChanged(const string16& text,
                                                 size_t offset,
                                                 const ui::Range& range) {
@@ -432,11 +442,17 @@ void RenderWidgetHostViewBase::UpdateScreenInfo(gfx::NativeView view) {
   if (current_display_area_ == display.work_area() &&
       current_device_scale_factor_ == display.device_scale_factor())
     return;
+
+  bool device_scale_factor_changed =
+      current_device_scale_factor_ != display.device_scale_factor();
   current_display_area_ = display.work_area();
   current_device_scale_factor_ = display.device_scale_factor();
-  if (impl)
+  if (impl) {
+    if (device_scale_factor_changed)
+        impl->WasResized();
     impl->NotifyScreenInfoChanged();
   }
+}
 
 SmoothScrollGesture* RenderWidgetHostViewBase::CreateSmoothScrollGesture(
     bool scroll_down, int pixels_to_scroll, int mouse_event_x,