supersize: Add "diff" command

tools/binary_size/libsupersize/testdata/Console.golden

+# Show pydoc for main types:
+import models
+help(models)
+
+# Show all attributes of all symbols & per-section totals:
+Print(size_info, verbose=True)
+
+# Show two levels of .text, grouped by first two subdirectories
+text_syms = size_info.symbols.WhereInSection("t")
+by_path = text_syms.GroupBySourcePath(depth=2)
+Print(by_path.WhereBiggerThan(1024))
+
+# Show all non-vtable generated symbols
+generated_syms = size_info.symbols.WhereIsGenerated()
+Print(generated_syms.WhereNameMatches(r"vtable").Inverted())
+
+# Show all symbols that have "print" in their name or path, except
+# those within components/.
+# Note: Could have also used Inverted(), as above.
+# Note: Use "help(ExpandRegex)" for more about what {{_print_}} does.
+print_syms = size_info.symbols.WhereMatches(r"{{_print_}}")
+Print(print_syms - print_syms.WherePathMatches(r"^components/"))
+
+# Diff two .size files and save result to a file:
+Print(Diff(size_info1, size_info2), to_file="output.txt")
+
+Metadata:
+
+Section Sizes (Total=43,785,380 bytes):
+    .bss: 1,300,456 bytes (not included in totals)
+    .data: 101,768 bytes (0.2%)
+    .data.rel.ro: 1,065,224 bytes (2.4%)
+    .data.rel.ro.local: 790,024 bytes (1.8%)
+    .rodata: 5,927,652 bytes (13.5%)
+    .text: 35,900,712 bytes (82.0%)
+
+Showing 38 symbols with total size: 2652506 bytes
+.text=10.3kb     .rodata=2.52mb     other=388 bytes  total=2.53mb
+Number of object files: 10
+
+First columns are: running total, type, size
+ 2641394 r@Group      2641394 {no path}
+             ** merge strings (count=2)
+ 2651152 t@Group      9758    {no path}
+             ** symbol gaps (count=2)
+ 2651600 t@0x28f000   448     third_party/icu/ucnv_ext.c
+             ucnv_extMatchFromU
+ 2651752 d@0x2de7008  152     third_party/container.c
+             rel._ZN4base7androidL22kBaseRegisteredMethodsE
+ 2651846 t@0x2a1000   94      third_party/container.c
+             blink::PaintChunker::releasePaintChunks [clone .part.1]
+ 2651902 d@0x2c176f0  56      third_party/icu/ucnv_ext.c
+             ChromeMainDelegate [vtable]
+ 2651958 d@0x2cd8500  56      third_party/paint.cc
+             ChromeMainDelegateAndroid [vtable]
+ 2652014 t@0x28d910   56      base/page_allocator.cc
+             startup._GLOBAL__sub_I_bbr_sender.cc
+ 2652069 r@0x28f3450  55      third_party/paint.cc
+             kAnimationFrameTimeHistogramClassPath
+ 2652113 r@0x284e370  44      base/page_allocator.cc
+             Name
+ 2652151 t@0x28d964   38      base/page_allocator.cc
+             extFromUUseMapping
+ 2652183 r@0x284e398  32      third_party/container.c
+             chrome::mojom::FilePatcher::Name_
+ 2652215 t@0x28d98a   32      base/page_allocator.cc
+             extFromUUseMapping
+ 2652243 t@0x2a0020   28      third_party/container.c
+             blink::ContiguousContainerBase::ContiguousContainerBase
+ 2652271 t@0x28f1c8   28      third_party/icu/ucnv_ext.c
+             startup._GLOBAL__sub_I_SkDeviceProfile.cpp
+ 2652299 t@0x28d948   28      base/page_allocator.cc
+             startup._GLOBAL__sub_I_pacing_sender.cc
+ 2652323 d@0x2c17740  24      third_party/container.c
+             chrome::mojom::FieldTrialRecorderProxy [vtable]
+ 2652347 d@0x2c17728  24      third_party/icu/ucnv_ext.c
+             chrome::mojom::FieldTrialRecorderRequestValidator [vtable]
+ 2652371 d@0x2cd8538  24      base/page_allocator.cc
+             mojo::MessageReceiver [vtable]
+ 2652395 t@0x28f1e0   24      third_party/icu/ucnv_ext.c
+             startup._GLOBAL__sub_I_SkDiscardableMemoryPool.cpp
+ 2652411 d@0x2cd84e0  16      third_party/gvr-android-sdk/libgvr_shim_static_arm.a/libcontroller_api_impl.a_controller_api_impl.o
+             .Lswitch.table.45
+ 2652427 t@0x2a0000   16      third_party/paint.cc
+             blink::ContiguousContainerBase::shrinkToFit
+ 2652443 t@0x28d900   16      base/page_allocator.cc
+             startup._GLOBAL__sub_I_page_allocator.cc
+ 2652455 t@0x2a0010   12      third_party/paint.cc
+             blink::ContiguousContainerBase::shrinkToFit [clone .part.1234] [clone .isra.2]
+ 2652467 d@0x2cd8550  12      base/page_allocator.cc
+             kMethodsAnimationFrameTimeHistogram
+ 2652478 r@0x284e364  11      base/page_allocator.cc
+ 2652486 d@0x2cd84f0  8       third_party/gvr-android-sdk/libgvr_shim_static_arm.a/libport_android_jni.a_jni_utils.o
+             kSystemClassPrefixes
+ 2652490 d@0x2de70a0  4       third_party/container.c
+             base::android::g_renderer_histogram_code
+ 2652494 r@0x28f3480  4       third_party/paint.cc
+             blink::CSSValueKeywordsHash::findValueImpl::value_word_list
+ 2652498 d@0x2de7000  4       base/page_allocator.cc
+             google::protobuf::internal::pLinuxKernelCmpxchg
+ 2652502 d@0x2de7004  4       third_party/container.c
+             google::protobuf::internal::pLinuxKernelMemoryBarrier
+ 2652506 d@0x2de70a4  4       third_party/container.c
+             rel.local._ZN4base7android12_GLOBAL__N_124g_library_version_numberE
+ 2652506 b@0x0        262144  third_party/fft_float.cc
+             ff_cos_131072
+ 2652506 b@0x0        131072  third_party/fft_fixed.cc
+             ff_cos_131072_fixed
+ 2652506 b@0x0        131072  third_party/fft_float.cc
+             ff_cos_65536
+ 2652506 b@0x2dffe80  200     third_party/icu/ucnv_ext.c
+             SaveHistogram::atomic_histogram_pointer
+ 2652506 b@0x2dffda0  28      third_party/icu/ucnv_ext.c
+             g_chrome_content_browser_client
+ 2652506 b@0x2dffe84  4       third_party/icu/ucnv_ext.c
+             g_AnimationFrameTimeHistogram_clazz