Bug 814778: Disable font inflation for the b2g master process. r=dbaron

b2g/app/b2g.js

@@ -585,6 +585,8 @@ pref("jsloader.reuseGlobal", true);
 
 // Enable font inflation for browser tab content.
 pref("font.size.inflation.minTwips", 120);
+// And disable it for lingering master-process UI.
+pref("font.size.inflation.disabledInMasterProcess", true);
 
 // Enable freeing dirty pages when minimizing memory; this reduces memory
 // consumption when applications are sent to the background.

layout/base/nsIPresShell.h

@@ -1298,6 +1298,10 @@ public:
     return mFontSizeInflationForceEnabled;
   }
 
+  bool FontSizeInflationDisabledInMasterProcess() const {
+    return mFontSizeInflationDisabledInMasterProcess;
+  }
+
   virtual void AddInvalidateHiddenPresShellObserver(nsRefreshDriver *aDriver) = 0;
 
   void InvalidatePresShellIfHidden();
@@ -1450,6 +1454,7 @@ protected:
   uint32_t mFontSizeInflationMinTwips;
   uint32_t mFontSizeInflationLineThreshold;
   bool mFontSizeInflationForceEnabled;
+  bool mFontSizeInflationDisabledInMasterProcess;
 
   // The maximum width of a line box. Text on a single line that exceeds this
   // width will be wrapped. A value of 0 indicates that no limit is enforced.

layout/base/nsLayoutUtils.cpp

@@ -111,6 +111,7 @@ typedef FrameMetrics::ViewID ViewID;
 /* static */ int32_t  nsLayoutUtils::sFontSizeInflationMappingIntercept;
 /* static */ uint32_t nsLayoutUtils::sFontSizeInflationMaxRatio;
 /* static */ bool nsLayoutUtils::sFontSizeInflationForceEnabled;
+/* static */ bool nsLayoutUtils::sFontSizeInflationDisabledInMasterProcess;
 
 static ViewID sScrollIdCounter = FrameMetrics::START_SCROLL_ID;
 
@@ -4773,6 +4774,8 @@ nsLayoutUtils::Initialize()
                               "font.size.inflation.mappingIntercept");
   Preferences::AddBoolVarCache(&sFontSizeInflationForceEnabled,
                                "font.size.inflation.forceEnabled");
+  Preferences::AddBoolVarCache(&sFontSizeInflationDisabledInMasterProcess,
+                               "font.size.inflation.disabledInMasterProcess");
 
 #ifdef MOZ_FLEXBOX
   Preferences::RegisterCallback(FlexboxEnabledPrefChangeCallback,
@@ -5157,10 +5160,20 @@ nsLayoutUtils::FontSizeInflationEnabled(nsPresContext *aPresContext)
        aPresContext->IsChrome()) {
     return false;
   }
-  if (TabChild* tab = GetTabChildFrom(presShell)) {
-    if (!presShell->FontSizeInflationForceEnabled() &&
-        !tab->IsAsyncPanZoomEnabled()) {
-      return false;
+  // Force-enabling font inflation always trumps the heuristics here.
+  if (!presShell->FontSizeInflationForceEnabled()) {
+    if (TabChild* tab = GetTabChildFrom(presShell)) {
+      // We're in a child process.  Cancel inflation if we're not
+      // async-pan zoomed.
+      if (!tab->IsAsyncPanZoomEnabled()) {
+        return false;
+      }
+    } else if (XRE_GetProcessType() == GeckoProcessType_Default) {
+      // We're in the master process.  Cancel inflation if it's been
+      // explicitly disabled.
+      if (presShell->FontSizeInflationDisabledInMasterProcess()) {
+        return false;
+      }
     }
   }
 

layout/base/nsLayoutUtils.h

@@ -1652,6 +1652,10 @@ public:
     return sFontSizeInflationForceEnabled;
   }
 
+  static bool FontSizeInflationDisabledInMasterProcess() {
+    return sFontSizeInflationDisabledInMasterProcess;
+  }
+
   /**
    * See comment above "font.size.inflation.mappingIntercept" in
    * modules/libpref/src/init/all.js .
@@ -1771,6 +1775,7 @@ private:
   static int32_t  sFontSizeInflationMappingIntercept;
   static uint32_t sFontSizeInflationMaxRatio;
   static bool sFontSizeInflationForceEnabled;
+  static bool sFontSizeInflationDisabledInMasterProcess;
 };
 
 template<typename PointType, typename RectType, typename CoordType>

layout/base/nsPresShell.cpp

@@ -9196,6 +9196,7 @@ PresShell::SetupFontInflation()
   mFontSizeInflationMinTwips = nsLayoutUtils::FontSizeInflationMinTwips();
   mFontSizeInflationLineThreshold = nsLayoutUtils::FontSizeInflationLineThreshold();
   mFontSizeInflationForceEnabled = nsLayoutUtils::FontSizeInflationForceEnabled();
+  mFontSizeInflationDisabledInMasterProcess = nsLayoutUtils::FontSizeInflationDisabledInMasterProcess();
 }
 
 void

modules/libpref/src/init/all.js

@@ -1796,6 +1796,16 @@ pref("font.size.inflation.minTwips", 0);
  * either of the prefs above.  It has no meaning in single-mode UIs.
  */
 pref("font.size.inflation.forceEnabled", false);
+/*
+ * In products with multi-mode pan-and-zoom and non-pan-and-zoom UIs,
+ * this pref disables font inflation in master-process contexts where
+ * existing heuristics can't be used determine enabled-ness.
+ *
+ * This pref has no effect if font inflation is not enabled through
+ * either of the prefs above.  The "forceEnabled" pref above overrides
+ * this pref.
+ */
+pref("font.size.inflation.disabledInMasterProcess", false);
 /*
  * Since the goal of font size inflation is to avoid having to
  * repeatedly scroll side to side to read a block of text, and there are