Touch emulator: enables double tap support for pages similar to Chrome on Android.

content/browser/renderer_host/dip_util.cc

Index: content/browser/renderer_host/dip_util.cc
diff --git a/content/browser/renderer_host/dip_util.cc b/content/browser/renderer_host/dip_util.cc
index 225d17bcb44f8733049a79adc6c1ca29ba51de89..95330ab5f797d30e809395de1433fc35eef16367 100644
--- a/content/browser/renderer_host/dip_util.cc
+++ b/content/browser/renderer_host/dip_util.cc
@@ -4,6 +4,7 @@
 
 #include "content/browser/renderer_host/dip_util.h"
 
+#include "cc/output/compositor_frame_metadata.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "ui/base/layout.h"
 #include "ui/gfx/display.h"
@@ -16,6 +17,28 @@
 #include "ui/gfx/geometry/size_conversions.h"
 #include "ui/gfx/screen.h"
 
+namespace {
+
+// Used to accomodate finite precision when comparing scaled viewport and
+// content widths. While this value may seem large, width=device-width on an N7
+// V1 saw errors of ~0.065 between computed window and content widths.
+const float kMobileViewportWidthEpsilon = 0.15f;
+
+bool HasFixedPageScale(const cc::CompositorFrameMetadata& frame_metadata) {
+  return frame_metadata.min_page_scale_factor ==
+         frame_metadata.max_page_scale_factor;
+}
+
+bool HasMobileViewport(const cc::CompositorFrameMetadata& frame_metadata) {
+  float window_width_dip =
+      frame_metadata.page_scale_factor *
+          frame_metadata.scrollable_viewport_size.width();
+  float content_width_css = frame_metadata.root_layer_size.width();
+  return content_width_css <= window_width_dip + kMobileViewportWidthEpsilon;
+}
+
+}  // namespace
+
 namespace content {
 
 float GetScaleFactorForView(const RenderWidgetHostView* view) {
@@ -37,4 +60,14 @@ gfx::Rect ConvertViewRectToPixel(const RenderWidgetHostView* view,
   return gfx::ConvertRectToPixel(GetScaleFactorForView(view), rect_in_dip);
 }
 
+bool IsMobileOptimizedFrame(const cc::CompositorFrameMetadata& frame_metadata) {
+  // Disable double tap zoom for pages that have a width=device-width or
+  // narrower viewport (indicating that this is a mobile-optimized or responsive
+  // web design, so text will be legible without zooming). Also disable
+  // double tap and pinch for pages that prevent zooming in or out.
+  bool has_mobile_viewport = HasMobileViewport(frame_metadata);
+  bool has_fixed_page_scale = HasFixedPageScale(frame_metadata);
+  return !has_fixed_page_scale && !has_mobile_viewport;
+}
+
 }  // namespace content