Bug 1590639 part 1: Fix non-unified build issues in layout/generic. r=TYLin

The issues fall into these categories:
 - Files that used StaticPrefs::layout_XYZ() API or gfxVars::XYZ that needed an
   include. (Addressed by adding the missing include.)
 - Files that use mozilla::dom::XYZ or mozilla::gfx::XYZ without qualifying the
   namespace & without a 'using' decl. (Addressed by adding "using".)
 - A few other includes for types/inlines that were used without their header.

Depends on D50162

Differential Revision: https://phabricator.services.mozilla.com/D50163

--HG--
extra : moz-landing-system : lando

layout/generic/ScrollSnap.cpp

@@ -10,6 +10,7 @@
 
 #include "mozilla/Maybe.h"
 #include "mozilla/Preferences.h"
+#include "mozilla/StaticPrefs_layout.h"
 #include "nsLineLayout.h"
 
 namespace mozilla {

layout/generic/nsBlockFrame.cpp

@@ -17,6 +17,7 @@
 #include "mozilla/DebugOnly.h"
 #include "mozilla/Maybe.h"
 #include "mozilla/PresShell.h"
+#include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/ToString.h"
 #include "mozilla/UniquePtr.h"
 

layout/generic/nsColumnSetFrame.cpp

@@ -11,6 +11,7 @@
 #include "mozilla/ColumnUtils.h"
 #include "mozilla/Logging.h"
 #include "mozilla/PresShell.h"
+#include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/ToString.h"
 #include "nsCSSRendering.h"
 

layout/generic/nsFlexContainerFrame.cpp

@@ -7,6 +7,8 @@
 /* rendering object for CSS "display: flex" */
 
 #include "nsFlexContainerFrame.h"
+
+#include "nsBlockFrame.h"
 #include "nsContentUtils.h"
 #include "nsCSSAnonBoxes.h"
 #include "nsDisplayList.h"

layout/generic/nsFontInflationData.cpp

@@ -12,6 +12,7 @@
 #include "nsTextControlFrame.h"
 #include "nsListControlFrame.h"
 #include "nsComboboxControlFrame.h"
+#include "mozilla/dom/Text.h"  // for inline nsINode::AsText() definition
 #include "mozilla/PresShell.h"
 #include "mozilla/ReflowInput.h"
 #include "nsTextFrameUtils.h"

layout/generic/nsFrame.cpp

@@ -53,6 +53,7 @@
 #include "nsLayoutUtils.h"
 #include "LayoutLogging.h"
 #include "mozilla/RestyleManager.h"
+#include "nsImageFrame.h"
 #include "nsInlineFrame.h"
 #include "nsFrameSelection.h"
 #include "nsGkAtoms.h"
@@ -126,7 +127,6 @@ using namespace mozilla::gfx;
 using namespace mozilla::layers;
 using namespace mozilla::layout;
 typedef nsAbsoluteContainingBlock::AbsPosReflowFlags AbsPosReflowFlags;
-class nsImageFrame;
 
 const mozilla::LayoutFrameType nsIFrame::sLayoutFrameTypes[
 #define FRAME_ID(...) 1 +

layout/generic/nsGfxScrollFrame.cpp

@@ -21,6 +21,7 @@
 #include "nsGkAtoms.h"
 #include "nsNameSpaceManager.h"
 #include "mozilla/dom/DocumentInlines.h"
+#include "mozilla/gfx/gfxVars.h"
 #include "nsFontMetrics.h"
 #include "nsBoxLayoutState.h"
 #include "mozilla/dom/NodeInfo.h"

layout/generic/nsSubDocumentFrame.cpp

@@ -31,6 +31,8 @@
 #include "nsViewManager.h"
 #include "nsGkAtoms.h"
 #include "nsStyleConsts.h"
+#include "nsStyleStruct.h"
+#include "nsStyleStructInlines.h"
 #include "nsFrameSetFrame.h"
 #include "nsIScrollable.h"
 #include "nsNameSpaceManager.h"
@@ -53,8 +55,9 @@
 #include "mozilla/layers/RenderRootStateManager.h"
 
 using namespace mozilla;
+using namespace mozilla::dom;
+using namespace mozilla::gfx;
 using namespace mozilla::layers;
-using mozilla::dom::Document;
 
 static Document* GetDocumentFromView(nsView* aView) {
   MOZ_ASSERT(aView, "null view");

layout/generic/nsTextFrameUtils.cpp

@@ -6,6 +6,7 @@
 
 #include "nsTextFrameUtils.h"
 
+#include "mozilla/dom/Text.h"
 #include "nsBidiUtils.h"
 #include "nsCharTraits.h"
 #include "nsIContent.h"
@@ -16,6 +17,7 @@
 #include <algorithm>
 
 using namespace mozilla;
+using namespace mozilla::dom;
 
 // static
 bool nsTextFrameUtils::IsSpaceCombiningSequenceTail(const char16_t* aChars,