Linux UI: Switch to the Gtk3 theme

Sets "use_gtk3 = true" by default.

BUG=79722
TBR=dpranke@chromium.org
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_chromium_msan_rel_ng;master.tryserver.chromium.linux:linux_chromium_dbg_32_ng

> > Review-Url: https://codereview.chromium.org/2670623002
> > Cr-Commit-Position: refs/heads/master@{#452118}
> > Committed: https://chromium.googlesource.com/chromium/src/+/872a494bba52e597388aec738d9d681183a3d47b

> Review-Url: https://codereview.chromium.org/2670623002
> Cr-Commit-Position: refs/heads/master@{#454491}
> Committed: https://chromium.googlesource.com/chromium/src/+/89be63a39b5014096115d3ec60d13fde39e73283

Review-Url: https://codereview.chromium.org/2670623002
Cr-Original-Commit-Position: refs/heads/master@{#455596}
Committed: https://chromium.googlesource.com/chromium/src/+/072522801041708fba94498a1844cb89f24d4590
Review-Url: https://codereview.chromium.org/2670623002
Cr-Commit-Position: refs/heads/master@{#458263}
diff --git a/build/config/linux/gtk/gtk.gni b/build/config/linux/gtk/gtk.gni
index b3fd973..0521a8c 100644
--- a/build/config/linux/gtk/gtk.gni
+++ b/build/config/linux/gtk/gtk.gni
@@ -7,6 +7,9 @@
 # //build/config/linux/gtk and it will switch for you.
 
 declare_args() {
-  # Whether to compile agains GTKv3 instead of GTKv2.
-  use_gtk3 = false
+  # Whether to compile against GTKv3 instead of GTKv2.
+  # TODO(thomasanderson): Currently, the 32-bit clusterfuzz schroot does not
+  # have libgtk-3-0 installed.  set use_gtk3 = true on all architectures when
+  # the package is added (crbug.com/699669).
+  use_gtk3 = target_cpu == "x64"
 }
diff --git a/chrome/installer/linux/debian/expected_deps_x64_jessie b/chrome/installer/linux/debian/expected_deps_x64_jessie
index 7f59311..3f76b8a 100644
--- a/chrome/installer/linux/debian/expected_deps_x64_jessie
+++ b/chrome/installer/linux/debian/expected_deps_x64_jessie
@@ -2,7 +2,7 @@
 libasound2 (>= 1.0.16)
 libatk1.0-0 (>= 1.12.4)
 libc6 (>= 2.15)
-libcairo2 (>= 1.2.4)
+libcairo2 (>= 1.6.0)
 libcups2 (>= 1.4.0)
 libdbus-1-3 (>= 1.1.4)
 libexpat1 (>= 2.0.1)
@@ -12,9 +12,9 @@
 libgconf-2-4 (>= 3.2.5)
 libgdk-pixbuf2.0-0 (>= 2.22.0)
 libglib2.0-0 (>= 2.28.0)
-libgtk2.0-0 (>= 2.24.0)
-libnspr4 (>= 2:4.9-2~) | libnspr4-0d (>= 1.8.0.10)
-libnss3 (>= 2:3.13.4-2~) | libnss3-1d (>= 3.12.4)
+libgtk-3-0 (>= 3.3.16)
+libnspr4 (>= 2:4.9-2~)
+libnss3 (>= 2:3.13.4-2~)
 libpango-1.0-0 (>= 1.14.0)
 libpangocairo-1.0-0 (>= 1.14.0)
 libstdc++6 (>= 4.8.1)
diff --git a/chrome/installer/linux/debian/expected_deps_x64_wheezy b/chrome/installer/linux/debian/expected_deps_x64_wheezy
index 98c6bd6..cea1252 100644
--- a/chrome/installer/linux/debian/expected_deps_x64_wheezy
+++ b/chrome/installer/linux/debian/expected_deps_x64_wheezy
@@ -2,7 +2,7 @@
 libasound2 (>= 1.0.16)
 libatk1.0-0 (>= 1.12.4)
 libc6 (>= 2.11)
-libcairo2 (>= 1.2.4)
+libcairo2 (>= 1.6.0)
 libcups2 (>= 1.4.0)
 libdbus-1-3 (>= 1.1.4)
 libexpat1 (>= 2.0.1)
@@ -11,8 +11,8 @@
 libgcc1 (>= 1:4.1.1)
 libgconf-2-4 (>= 2.31.1)
 libgdk-pixbuf2.0-0 (>= 2.22.0)
-libglib2.0-0 (>= 2.26.0)
-libgtk2.0-0 (>= 2.24.0)
+libglib2.0-0 (>= 2.28.0)
+libgtk-3-0 (>= 3.3.16)
 libnspr4 (>= 2:4.9-2~) | libnspr4-0d (>= 1.8.0.10)
 libnss3 (>= 2:3.13.4-2~) | libnss3-1d (>= 3.12.4)
 libpango1.0-0 (>= 1.14.0)
diff --git a/chrome/installer/linux/rpm/expected_deps_x86_64 b/chrome/installer/linux/rpm/expected_deps_x86_64
index 5f6fb5a..ddaf415 100644
--- a/chrome/installer/linux/rpm/expected_deps_x86_64
+++ b/chrome/installer/linux/rpm/expected_deps_x86_64
@@ -36,13 +36,13 @@
 libgcc_s.so.1(GCC_3.0)(64bit)
 libgcc_s.so.1(GCC_4.0.0)(64bit)
 libgconf-2.so.4()(64bit)
-libgdk-x11-2.0.so.0()(64bit)
+libgdk-3.so.0()(64bit)
 libgdk_pixbuf-2.0.so.0()(64bit)
 libgio-2.0.so.0()(64bit)
 libglib-2.0.so.0()(64bit)
 libgmodule-2.0.so.0()(64bit)
 libgobject-2.0.so.0()(64bit)
-libgtk-x11-2.0.so.0()(64bit)
+libgtk-3.so.0()(64bit)
 libm.so.6()(64bit)
 libm.so.6(GLIBC_2.2.5)(64bit)
 libnspr4.so()(64bit)